the benefit of siblings at home

8/22/2019 The Benefit of Siblings at Home

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DOUGLAS B. DOWNEY AND DENNIS J. CONDRONOhio State University

Playing Well with Others in Kindergarten:

The Benefit of Siblings at Home

There are many reasons to expect that childrengain something by growing up with siblings, yetthere is surprisingly scant evidence of this advan-tage. Indeed, the vast majority of research asses-sing the consequences of siblings reports negativeeffects: Children with many siblings do not performas well in school as children with few siblings. By

focusing almost exclusively on educational out-comes, however, previous studies have neglected

ways in which children might benefit from siblings.One possibility, for example, is that siblings pro-mote childrens social and interpersonal skills. Inthis study, we analyze a sample of kindergartners(N 20,649) from The Early Childhood Longitu-dinal StudyKindergarten Class of 199899 toreplicate the often-noted negative relationshipbetween number of siblings and cognitive out-comes, and then demonstrate that this patterndoes not extend to social skills. Findings are con-sistent with the view that children negotiate peer

relationships better when they grow up with atleast one sibling.

The growth in the divorce rate in the 1970s andthe more recent increase in cohabitation havedominated demographers attention. But house-holds have changed in another way, too. Thesteady decline in fertility means that an increas-ing percentage of children are growing up with

few siblings. Although the consequences of thisdemographic change are not yet fully understood,available research suggests that most children areprobably better off because additional siblingstend to dilute parental resources such as time,energy, and money (Blake, 1989; Downey,1995). On balance, the current evidence suggestssurprisingly few advantages to additionalsiblings, especially having several siblings. The

majority of scholarship in this area, however, hasfocused on the relationship between sibship sizeand educational outcomes and has devoted lessattention to the possibility that having siblingspromotes social and interpersonal skills. In thisstudy, we extend our understanding of how sib-ship size matters by documenting its relationshipwith social and interpersonal skills in a nationallyrepresentative sample of kindergartners.

SIBLINGS AND SOCIAL SKILLS:TWO PERSPECTIVES

Resource Dilution

Most social science discourse on the effect ofsiblings is shaped in some form by the simpleideas espoused in the resource dilution model.Beginning with the assumption that parentalresources are finite, the model posits that as thenumber of children in the household increases, the

proportion of parental resources accrued by anyone child decreases (Blake, 1989; Downey, 2001).Blake (1981a), a leading proponent of the resourcedilution perspective, outlined three types of finiteparental resources: (a) types of homes, necessities

Department of Sociology, 300 Bricker Hall, 190 N. Oval

Mall, The Ohio State University, Columbus, OH 43210

([email protected]).

Key Words: children, siblings, social skills.

Journal of Marriage and Family 66 (May 2004): 333350 333


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of life, cultural objects (like books, pictures,music, and so forth), (b) personal attention,intervention, and teaching, and (c) specificchances to engage the outside world (p. 422).Blake suggested that [t]he more children, themore these resources are divided (even taking

account of economies of scale) and hence, thelower the quality of the output (p. 422).

Dilution proponents suggest that, on average,children do not benefit from having siblingsbecause siblings dilute rather than provideresources. As evidence for this position, theypoint to the many studies reporting an inverserelationship between siblings and a wide range ofeducational outcomes such as years of educationattained and math and verbal test scores (Blake,1981a, 1989; Downey, 1995; Zajonc & Markus,1975). In nearly every case, it appears that chil-dren do better in school and on cognitive testswhen they have fewer versus many siblings.

The evidence that siblings reduce educationalachievement is not completely without excep-tions, however. Only children sometimes performworse than children with one or two siblings,providing at least a hint that children may enjoyeducational benefits from having small numbersof siblings. Zajonc and Markus (1975) arguedthat this benefit is real, explaining that only chil-dren (and lastborns) are disadvantaged by lackinga younger sibling to teach. Blake (1989),however, argued that these apparent benefits arespurious. Blake suggested that only children insome samples do not perform as well as thosewith one sibling because only children have moreoften experienced family disruption and becausethey have defects (intellectual or otherwise) thatled parents to discontinue reproduction (p. 141).Her empirical work showed that the only-childexception was typically reduced or eliminatedwhen she statistically controlled for family struc-ture and indicators of the childs disability status.

Although developed with the goal of explainingdisparities in educational outcomes, the dilutionperspective also has implications for understandinghow siblings might influence childrens social andinterpersonal skills. Dilution theorists put primaryemphasis on how siblings affect available parentalresources, and are skeptical that siblings serve asresources. Blake (1989), for instance, stated that

the notion that older siblings typically, and onaverage, function in loco parentis assumes toomuch about sibling goodwill and maturity(p. 12). Along these lines, Perez-Granados andCallanan (1997) found that older siblings were

less successful at teaching their younger siblingsinformation than were the childrens mothers.Taken as a whole, resource dilution theory viewssiblings primarily as competitors for parentalresources and as poor providers of resourcesthemselves. From this perspective, childrens

social skills should also decline as sibship sizeincreases.

Of course, dilution theory arguments are mostappealing when the focus is on finite parentalresources that are not easily shared by siblings.For example, Downey (1995) found that siblingshave a stronger effect on money saved for collegethan on the frequency with which parents speakwith their children. Money saved for collegerepresents a finite resource that, once used, can-not be enjoyed by other siblings. In contrast, thefrequency with which parents speak with theirchildren is a resource that parents could morereadily expand as sibship size grows, and couldpotentially be shared among siblings (e.g., par-ents interact with all of their progeny at the sametime). For our purposes, the resources parentsprovide that promote childrens social skills areunlikely to be as strictly finite as money savedfor college. Consequently, if the dilution modelcorrectly predicts a negative association betweensibship size and social skills, we would expect amore modest relationship than that observedbetween sibship size and money saved for college.

Siblings as Resources

An alternative position is that siblings are not justcompetitors for parental resources, but that chil-dren actually gain interpersonal skills from thepresence of brothers and sisters. The argumenthere is that through repeated interactions withsiblings, children are forced to develop inter-personal skills that can then be generalized to peerrelationships (MacKinnon, Starnes, Volling, &Johnson, 1997; McCoy, Brody, & Stoneman, 1994).

Brody (1998) described how siblings provideopportunities for play that encourage the under-standing of roles:

In learning and practicing a role, a child learnsnot only his or her own role, but also the com-plimentary ones. Naturalistic observations ofsibling interactions indicate that siblings enactasymmetrical, complimentary roles with oneanother. Older siblings act as teachers, managers,and helpers when playing with their youngerbrothers and sisters, and the younger siblingsassume the corresponding learner, managee,and helpee roles (p. 16).

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Siblings do not always get along, of course, butconflict at home can be training for negotiatingrelationships in other contexts by allowingchildren to hone communication skills and con-vey feelings or emotions (Brody, 1998). Alongthese same lines, Polit and Falbo (1987) de-

scribed the disadvantages of not having at leastone sibling in this way: Only children fail tolearn critical developmental lessons by not beingraised with siblings, and consequently would beexpected to fare worse than non-onlies in termsof such outcomes as personal adjustment, coop-erativeness, and ability to get along with peers(p. 319).

In direct contrast to the resource dilutionprediction, the siblings as resources positionsuggests that, all else being equal, children aremost likely to develop social skills in the largestfamilies. As sibship size grows, the opportunityfor greater sibling interaction increases; thus,additional siblings should be associated withimproved social skills. A modification of thisposition is that children gain social skills fromsibling interactions, but this benefit is fulfilled byreaching a particular threshold of siblings. Evenone sibling may provide all of the necessary sib-ling interaction needed to develop social skills. Ifso, additional siblings after one may increase thenumber of sibling interactions but not necessarilypromote social skills because the threshold fornecessary sibling interaction has been met witha single sibling. This view is popular among thepublic (Blake, 1981b) and has motivated manyresearchers to focus their attention on distinctionsbetween children with zero versus one sibling(s).

Another possibility is that children benefit themost from parent-supervised sibling interactions.Because the amount of time parents spend withtheir children declines as sibship size increases(Downey, 1995; Hill & Stafford, 1974), there isreason to expect that the proportion of siblinginteractions that go unsupervised increases as sib-ship size grows. If children gain the most fromsibling interactions when they are refereed by aparent, then a sibship of two or three childrenwould be the size most conducive to the devel-opment of social skills. From this perspective,unsupervised sibling interactions too often degen-erate into spats that result in little development of

social skills. As an example, lacking parentalsupervision, sibling disputes may be won bythe older sibling through brute force, with neithersibling developing effective social skills from theinteraction.

Parents intervention can be useful for childrento learn basic principles for resolving disputes(e.g., Use your words instead of hitting) andfor imagining how their behavior affects others(e.g., Why do you think your brother is upsetright now?). To the extent that parents prompt

their children to take the role of the other duringsibling interactions, children may be able togeneralize these social skills to other contextsthrough interactions with peers. It is not somuch the quantity of sibling interaction thatmatters, the argument goes, but quality interactionas indicated by parent supervision. Based on theassumption that supervised sibling interactionsoccur more frequently in small sibships, thisperspective predicts that the benefit of siblingswould be evident when comparing those withsmall numbers of siblings (e.g., one or two sib-lings) to those with no siblings, but would waneas sibship size increases and the proportion ofunsupervised sibling interactions grows.

THE CURRENT EVIDENCE

There has been remarkably little research on therelationship between sibship size and socialskills, but existing evidence suggests little social

skills benefit from having even one sister orbrother (Blake, 1981b, 1989; Polit & Falbo,1987). Polit and Falbo have provided the mostextensive review of literature studying the per-sonality characteristics of only children. Theirmeta-analysis examined 141 studies of only chil-drens personality characteristics and reported norelationship between number of siblings and peerpopularity (measured as the sociometric choicesof classmates) among 21 studies addressing thisissue. This seemingly convincing evidence isactually quite modest, however, given that thestudies included in their meta-analysis were, bythe authors own standards, of below averagequality in terms of sample size, probability sam-pling, multivariate methods, and the use of reli-able measurement scales.

Other more recent studies using small sampleshave found more mixed evidence. On one hand,Kitzmann, Cohen, and Lockwood (2002) studied139 children of elementary school age and foundthat, whereas only children had similar numbersof friends as children with one or two siblings,they were less liked by their classmates. Theauthors concluded that having a sibling maybe especially helpful for learning to manage

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conflict (p. 299). On the other hand, Riggio(1999) found no difference in social andemotional sensitivity, expressivity, and controlbetween 146 adults with and 51 adults withoutsiblings. There is some evidence that siblingshelp buffer stressful events. Kempton, Armistead,

Wierson, and Forehand (1991) found thatteachers ratings of children who had experienceda divorce were more positive for those with asibling than for children lacking a sibling.

One reason for the discrepancy among thesestudies may be that they rely on small samplesof questionable generalizability. Few studieshave assessed the relationship between siblingsand social skills with nationally representativedata, but one exception is Blake, Richardson,and Bhattacharyas (1991) study of adults fromthe 1957 Study of American Family Growth andthe 1976 survey Americans View Their MentalHealth. Noting that the review by Polit and Falbo(1987) suggested that children do not appearmore sociable as sibship size increases, Blakeet al. (1991) found a similar pattern in theirstudy of adults and concluded that the combina-tion of these two sets of findings suggests thatthere may be no effect of sibling number onsociability at any age (p. 280). The main con-cern with this work, however, is that Blakeet al.s indicators were of sociability, not socialskills. These indicators involved self-reportedresponses to questions that primarily addressedhow important friendships are and how importantit is to work with a nice group. Although thesemay capture one dimension of sociability, we aremore interested in whether individuals are skilledin their dealings with others and less interestedin whether they report valuing friends and nicegroups. Individuals could, for example, reportthat friendships are important to them but haveonly modest skills in actually maintaining goodfriendships.

Perhaps the most persuasive evidence thatadditional siblings affect family life is found inBaydar, Hyle, and Brooks-Gunns (1997) studyof children in the National Longitudinal Surveyof Youth. The authors compared children whogained a sibling to those who did not over a4-year period on a wide range of outcomes.They noted that, among families experiencing

an additional birth, the mother frequently adopteda controlling parenting style, and the childs ver-bal development appeared to suffer. Of note forour concerns, however, the authors also reportedsome evidence that childrens social skills were

affected by the new sibling. Consistent with otherstudies noting the difficulty of adjusting to anew sibling (Dunn & Munn, 1985), Baydar et al.(1997) reported that in the first 2 years after thebirth of a sibling, the older child exhibits greaterdifficulty relating to peers, as evaluated by the

parent. But after this initial adjustment period, theauthors found evidence of improving peer relationsconsistent with Stewarts (1990) claim that theprocess of adjusting to a new sibling may providean important developmental experience.

EXTENDING PAST WORK

Taken as a whole, there is little evidence thatchildren develop greater social and interpersonal

skills as their sibship size increases. There areimportant reasons for exploring this issue further,however. One hurdle is developing a convincingmeasure of social skills. Self-reports may be par-ticularly misleading if unskilled individuals areunaware of their deficits. Parents evaluations areof some value because they have spent so muchtime with their children, but these likely gaugechildrens interactions with siblings more so thanwith peers. If we are interested in whether sib-lings help children learn social skills that have

currency in contexts other than the home, third-party evaluations are most useful. In this regard,Polit and Falbos (1987) meta-analysis is note-worthy because the studies they evaluatedemployed sociometric measures of popularitybased on peer reports, a compelling measure ofsocial skills. Along these same lines, our indica-tors of childrens social skills come from a thirdparty (teachers) in a context separate from thehome (the classroom). Our data also have infor-mation from parents regarding their childrens

social skills. Parent and teacher reports of socialskills correlate in the expected direction, but theyare not always in accord, a point we return to inthe discussion.

We add to what is currently known about sib-ship size and social skills in three ways. First, thepotential benefit of siblings for social skills maynot have been observed in past studies becausethey were typically based on small, nongeneral-izable samples (e.g., one classroom), and thepattern reported by Polit and Falbo (1987) is notconsistently replicated (e.g., Kitzmann et al.,2002). Our analyses of generalizable data thatemploy third-party evaluations of childrens socialskills may help to resolve these discrepancies.



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Second, past research has not given dueconsideration to the possibility that any relation-ship between sibship size and social skills may bespurious. Parents who have many children areprobably different from parents who have fewchildren, a possibility that has led researchers to

suspect that the negative association betweensibship size and cognitive skills may be spurious(Downey, 2001; Downey, Powell, Steelman, &Pribesh, 1999; Ernst & Angst, 1983; Guo & VanWey, 1999; Rodgers, 2001). This issue of selec-tivity also clouds our attempt to discern whethersiblings have a causal effect on social skills. Ifselectivity works the way that past researchershave suggested, we would expect children withmany siblings to show poorer social skills thanchildren with few siblings because parents whohave many children are disadvantaged relative tothose who have few children.

Our study does not resolve whether sibshipsize has real consequences for children, but wecontribute to our understanding of how selectiv-ity matters by assessing whether the covariatesthat explain much (sometimes all) of the sibshipsize and educational outcome relationship can dothe same for social skills. The covariates we usein our study represent well-known differencesbetween the kinds of parents who have fewversus many children, and they are importantmediators of the link between sibship size andeducational outcomes. One argument is that,because of marital discord and eventual termina-tion, or the fact that the parents never married,children with no siblings more frequently comefrom single-parent households than do childrenwith any siblings. Accordingly, we controlled forfamily structure in our models. In addition, somescholars have suggested that parents may stophaving additional children after their first exhibitsdevelopmental problems (Blake, 1989). Toaccount for this possibility, we controlled forparental reports of whether the child has a dis-ability, the parents evaluation of the childshealth, and the childs birth weight. We alsoheld constant whether the child is currentlyenrolled in an afterschool program, given thatchildren with fewer siblings may more oftenenroll in these and potentially accrue social skillsbenefits from this experience.

But the more traditional argument is thatparents who produce many children are socio-economically disadvantaged relative to thosewho have few children (Ernst & Angst, 1983;Guo & Van Wey, 1999). To address this concern,

we included a control for socioeconomic statusbased on parents education, family income, andoccupations. We controlled for parents agebecause older parents generally have moreresources and may be more skilled in developingtheir childrens social skills. Finally, we con-

trolled for racial/ethnic group status. In supple-mental models (not shown), we also controlledfor indicators of religiosity and marital quality.These additional controls did not change the over-all pattern of results presented here. Althoughthere are likely still unmeasured differences (notincluded in our models) between parents withmany versus few children, associations betweensibship size and social skills independent of thewide range of covariates we employ wouldconstitute credible evidence that sibship sizeinfluences childrens development of social skills.

Finally, we see value in extending the study ofsibship size to include several of its theoreticallymeaningful components. In other words, althoughit is important to know whether adding anotherchild to the family shapes the development ofchildrens social skills, we can also ask whetherparticular kinds of siblings promote social skillsmore than others. Some evidence suggests thatthe influence of brothers (in brother pairs) ondelinquency is comparable to the influence ofsisters (in sister pairs; Slomkowski, Rende, Conger,Simons, & Conger, 2001), but it is not clearwhether the general effect of brothers and sisters(on both boys and girls) is similar. Studies consid-ering the general effect of brothers versus sistershave typically reported that brothers are moredamaging to school performance than are sisters(Powell & Steelman, 1990), and that brothersdilute parental resources for college more so thando sisters (Steelman & Powell, 1989). Studies have

also suggested that girls are rated as betterclassroom citizens than boys (Farkas, Grobe,Sheehan, & Shuan, 1990); we thus anticipate thatchildrens social skills will improve more fromexposure to sisters than to brothers.

We also consider birth order positioning andspacing. On one hand, past studies havesuggested that younger children benefit fromhaving older siblings (Brody & Murry, 2001),perhaps as a result of exposure to the oldersiblings social competencies. But older children

may also develop social skills through enactingthe teacher and helper role, an argument thatZajonc and Markus (1975) made with respect tocognitive skills. By taking the role of the other ininteractions with a younger sibling, older children



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may gain the ability to understand the perspectiveof the other (Brody, 1998). Closely spaced siblingsappear to be a greater liability than widely spacedones when predicting educational outcomes(Powell & Steelman, 1993)perhaps becausethey are more potent diluters of parental

resourcesbut they should provide more frequentinteraction partners at home, suggesting a poten-tially different pattern when predicting social skills.Rather than developing an aggregate measure ofsibling density, we follow Powell and Steelmans(1990) practice of distinguishing among siblings interms of both their birth order positions and thenumber of years from the target child.

In addition, sibling relationships may vary as aresult of genetic relatedness. Half siblings shareone fewer biological parent than full siblings, andthus may spend less time with each other as aresult of time spent with parents not residing inthe household. Because stepsiblings typicallymust overcome an initial adjustment period thatis often stressful for children (Hetherington,Bridges, & Insabella, 1998), we expect childrento benefit less from exposure to stepsiblings thanfull siblings. Although few researchers haveexplored these issues in depth, one exceptionsuggests more conflict and aggression betweenfull siblings than half or stepsiblings (Deater-Deckard & Dunn, 2002), perhaps representingmore engagement overall among full siblings.Whether this greater conflict and aggressionamong full sibling versus other sibling pairsresults in better or worse social skills in othercontexts merits further attention.

RESEARCH QUESTIONS

In the study reported here, we addressed three

main questions: (a) Do children with more sib-lings exhibit better social and interpersonal skillsthan children with fewer siblings? (b) Do asso-ciations between sibship size and social skillspersist despite statistically controlling for a widerange of covariates? (c) Are particular kinds ofsiblings more important than others for the devel-opment of social skills?

METHOD

Data

Most of what we know about the effect of sib-lings is from studies of high school students and

adults, because some of our best data havefocused on these groups. Recently, however, theNational Center for Education Statistics collecteda wide range of information from parents,teachers, and school officials for a nationallyrepresentative sample of 21,260 children attend-

ing kindergarten in the fall of 19981999 (TheEarly Childhood Longitudinal StudyKinder-garten Class of 199899, or ECLS-K). TheECLS-K employed a multistage probability sam-pling design in which roughly 1,000 schools weresampled, and about 25 students within eachschool were selected. Our analyses were basedon the 20,649 cases for which there was a validschool identifier (this excluded 611 cases). Weused information collected from parents,teachers, and the children in the spring of 1999,near the end of the kindergarten year, when thechildrens average age was 6 years and 2 months.Childrens cognitive skills were evaluated inuntimed one-on-one assessments, parent informa-tion came from telephone surveys, and teachersfilled out self-administered questionnaires. (Forfurther information on the details of the studydesign and sample collection procedures, see U.S.Department of Education, 2000.) Our samplewas 55% White, 15% Black, 18% Hispanic(includes both those designating a specific raceand those not), 6% Asian, and 5% individualswho identified with a different race. Nearly 1 in5 (17%) children in this young sample was anonly child. The modal number of siblings wasone (42%), 26% had two siblings, 10% hadthree siblings, and 5% had four or more siblings.Two thirds of the sample lived in a householdwith both biological parents.

Dependent Variables

To measure childrens social and interpersonalskills, we made use of several reliable scalesconstructed by ECLS-K. (Unfortunately, ECLS-Kdoes not allow us, even with the restricted-usedata, to predict each individual item in thesescales.) See Table 1 for names, means, standarddeviations (when appropriate), and reliabilityscores (when appropriate) for all variables usedin this study.

Interpersonal skills. Teachers were asked to assesschildrens ability to (a) form and maintain friend-ships, (b) get along with people who are different,(c) comfort or help other children, (d) expressfeelings, ideas, and opinions in a positive way, and



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(e) show sensitivity to the feelings of others. Thismeasure ranges from 1 (neverto all items) to 4 (veryoften to all items), with a reliability ofa .89.

Self-control. Teachers rated the ability of thechildren to (a) control behavior by respectingthe property rights of others, (b) control temper,(c) accept peer ideas for group activities, and (d)respond appropriately to pressure from peers.This measure also ranges from 1 (never to all

items) to 4 (very often to all items), and has areliability ofa .80.

Externalizing problem behaviors. Teachers ratedthe frequency with which the child (a) argues, (b)fights, (c) gets angry, (d) acts impulsively, and(e) disturbs ongoing activities. Again, the range is1 (neverto all items) to 4 (very often to all items),and the reliability is high (a .90).

Reading skills. The reading assessment tested

five levels of proficiency: (a) identifying upper-and lowercase letters of the alphabet by name, (b)identifying letters with sounds at the beginning ofwords, (c) identifying letters with sounds at theend of words, (d) recognizing common words bysight, and (e) reading words in context. The read-ing Item Response Theory (IRT) scale in oursample ranges from 10 to 70 and has a reliabilityofa .93.

Math skills. The math assessment gauged chil-

drens ability to (a) identify numbers, (b) count,(c) recognize numbers in a sequence, and (d)perform simple addition and subtraction. Themath IRT scale scores range from 6 to 60, witha reliability ofa .92.

Independent Variables

Sibship size. We gathered information regardingsiblings from two sources. First, parents wereasked how many full, half, adopted, foster, andstepsiblings the target child has in the household.We based our dichotomous sibship size measureson parents responses to this question (e.g., zerosiblings, one sibling, two siblings, three siblings,four or more siblings). Second, parents wereasked for more detailed descriptions of all house-hold members, including information on siblings.We based our more detailed measures of the sib-ship (e.g., number of brothers and sisters, birthorder, age spacing, and so forth) on these

questions. In about 99% of the sample, informa-tion on siblings from these two sources was inagreement. Of the cases in which the two sourcesof information did not agree, the magnitude ofthe discrepancy was typically one sibling, and

TABLE 1

MEANS, STANDARD DEVIATIONS, AND ALPHAS FORVARIABLES USED IN THE ANALYSES: EARLY CHILDHOOD

LONGITUDINAL STUDY, KINDERGARTEN CLASS OF 199899(N 20,649)

Variable Name M SD

Dependent Variables

Interpersonal skills 3.10 .64 .89

Externalizing problem behaviors 1.68 .64 .90

Self control 3.16 .63 .80

Reading skills 30.38 14.49 .95

Math skills 26.99 9.46 .94

Sibship Measures

No siblings .17

One sibling .42

Two siblings .27

Three siblings .09

Four or more siblings .05

Number of brothers .76 .87

Number of sisters .73 .86

Siblings! 3 years older .49 .86

Siblings 12 years older .28 .48

Siblings within 1 year .16 .38

Siblings 12 years younger .16 .39

Siblings! 3 years younger .46 .62

Full siblings 1.28 1.14

Stepsiblings .03 .21

Half siblings .25 .60

Adopted and foster siblings .05 .29

Controls

Socioeconomic status 3.07 1.42

Parents age 34.20 6.72

Child lives with both biological parents .65

Child has disability .14

Childs age 74.67 4.50

Child in center care .20

Childs health 2.31 .82

Birth weight 7.35 1.34

White .55

Black .15

Hispanic .18

Asian .06

Other race .05

Note: These unweighted descriptive statistics are derived

from one of the five data sets with imputed missing values.



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analyses excluding these few cases producedresults similar to those reported here.

To test whether childrens sibship size isrelated to their social and interpersonal skills,we chose to use the aforementioned binary vari-ables, as opposed to a linear sibship size measure.

This approach allowed us to explore the possibil-ity that the relationship between sibship size andsocial skills is nonlinear, which is, in fact, whatmany theories predict. For instance, the resourcedilution perspective predicts a 1/x functionalrelationship between sibship size and outcomes.The possibility that children benefit from havingsiblings when a particular threshold of sibshipsize is reached also suggests a nonlinearrelationship, as does the possibility that childrenbenefit most when sibling interactions are super-vised by parents. In short, a linear sibship sizeterm runs the risk of masking these kinds ofpatterns.

Other dimensions of the sibship. Our primaryinterest is in how sibship size is related to socialskills, but partitioning the sibship into severaldimensions allows us to gain further insight intothe kinds of siblings that influence social skills.We split sibship size into number of brothers andnumber of sisters. We also developed a measurethat captures both age spacing and birth order byidentifying siblings as falling into one of fivecategories: (a) 3 or more years older, (b) 1 or 2years older, (c) within 1 year, (d) 1 or 2 yearsyounger, and (e) 3 or more years younger (seePowell & Steelman, 1990). Finally, we distin-guished between full, half, adopted, foster, andstepsiblings.

Controls. As noted above, families with manyversus few children might differ in importantways, and it is crucial to account for these factorsto isolate the effects of the sibship on childrenssocial and interpersonal skills. Toward that end,we controlled for the following: (a) a quintilemeasure of socioeconomic status based on par-ents education, occupational prestige, and familyincome (1 lowest, 5 highest); (b) racewhether the child is White (reference category),Black, Hispanic, Asian, or another race (0 no,1yes for each); (c) age of parentsthe averageof both parents ages when both have valid dataor one parents age when that is the only infor-mation available (19 youngest, 83 oldest); (d)family structurewhether the child lives withboth biological parents (0 no, 1yes); (e)

whether the child has a disability as reported bythe parent (0 no, 1yes); (f) the childs age inmonths (52.47 youngest, 102.30 oldest); (g)whether the child is currently enrolled in an after-school center-based program (0 no, 1yes);(h) the childs health on a scale (0poor,

4 excellent) reported by the parent; and (i) thechilds birth weight in pounds as reported bythe parent (1.0 to 13.7).

Analytic Strategy

We began by predicting childrens reading andmath scores in unadjusted and adjusted restrictedmaximum likelihood models, replicating the rela-tionship between sibship size and cognitive skillsreported in previous research (see Table 2). Thesemodels gave us confidence that our sample pro-duces results similar to past studies and that ourcontrol variables gauge important differencesbetween families with varying numbers of chil-dren.

We then predicted three teachers reports ofchildrens social skills: interpersonal skills, exter-nalizing problem behaviors, and self-control (seeTables 3, 4, and 5). For each dependent variable,we ran a series of models that employ differentmeasures of sibship size and composition. Webegan with sibship size, first entering severalbinary variables (one sibling, two siblings, threesiblings, four or more siblings), which allowed usto assess the effect of having each number ofsiblings with respect to having no siblings(Model 1). We then added the aforementionedcontrols to test whether any initial relationshipsbetween sibship size and social skills persist oncea wide variety of covariates are taken intoaccount (Model 2). Model 3 decomposed sibship

size into number of brothers and number ofsisters. Model 4 captured dimensions of birthorder and spacing. Finally, Model 5 estimatedthe effects of full, half, adopted, foster, and step-siblings. Although we removed children with nosiblings as a referent group in our models focus-ing on sibship size (Models 1 and 2), in Models35, no referent category was removed. Eachcoefficient in Models 35 therefore representsthe effect of having an additional sibling (ofthat type) versus not. For example, the coefficient

for number of brothers represents the effect ofhaving an additional brother versus not having anadditional brother.

To handle missing data, we performed multipleimputation, which imputed values five different



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times based on all variables included in the finalmodels and a random error component. (SeeAllison, 2002, for a useful explanation of theadvantages of multiple imputation.) Results basedon listwise deletion of missing data were similar. Inaddition, clustered sampling designs like that usedfor ECLS-K typically result in a sample with lessvariation among children than what would beobserved if children were drawn from the popula-

tion of all U.S. kindergartners using simple randomsampling. As a result, standard errors are typicallybiased downward, increasing the likelihood ofrejecting the null hypothesis. Our restricted max-imum likelihood models corrected the standarderrors for the clustering of students within schools,an adjustment that tends to increase the standarderrors by 10% to 40% and thus reduce the like-lihood of incorrectly rejecting a null hypothesis.

TABLE 2

RESTRICTED MAXIMUM LIKELIHOOD ESTIMATES OF CHILDRENS COGNITIVE SKILLS (N 20,649)

Reading Skills Math Skills

Unadjusted Adjusted Unadjusted Adjusted

One sibling (vs. none) .456

(.229)

.173

(.209)

.884**

(.189)

.260

(.166)

Two siblings (vs. none) 1.002**

(.236)

1.459**

(.227)

.189

(.188)

.351

(.173)

Three siblings (vs. none) 2.376**

(.339)

2.591**

(.318)

.485

(.273)

.850**

(.253)

Four or more siblings (vs. none) 4.827**

(.417)

4.571**

(.392)

2.579**

(.337)

2.477*

(.309)

Socioeconomic status 2.453**

(.067)

1.765**

(.057)

Parents age .054**(.013)

.054**(.009)

Child has disability (vs. does not) 2.673**

(.250)

2.630**

(.188)

Childs age .338**

(.018)

.411**

(.015)

Child in center care (vs. not) .360

(.217)

.457*

(.155)

Childs health .886**

(.098)

.584**

(.074)

Birth weight .262*

(.060)

.427**

(.046)Lives with both biological parents (vs. all other family types) .717**

(.190)

.781**

(.153)

Black (vs. White) .854**

(.275)

2.801**

(.216)

Hispanic (vs. White) 4.687**

(.246)

2.489**

(.185)

Asian (vs. White) .729*

(.357)

2.435**

(.264)

Other race (vs. White) .549

(.396)

1.699**

(.296)

Constant 30.16 6.57 26.23 14.39

Note: Standard errors are in parentheses.

*p< .01. **p< .001 (two-tailed tests).



10/18

TABLE 3

RESTRICTED MAXIMUM LIKELIHOOD ESTIMATES OF CHILDRENS INTERPERSONAL SKILLS (N 20,649)

Interpersonal Skills

Model 1 Model 2 Model 3 Model 4 Model 5

One sibling (vs. none) .112**

(.015)

.068**

(.015)

Two siblings (vs. none) .120**

(.014)

.073**

(.014)

Three siblings (vs. none) .074**

(.019)

.039

(.019)

Four or more siblings (vs. none) .054

(.025)

.030

(.024)

Number of brothers .005

(.006)

Number of sisters .002(.006)

Siblings! 3 years older .003

(.007)

Siblings 12 years older .020

(.010)

Siblings within 1 year .007

(.012)

Siblings 12 years younger .010

(.012)

Siblings! 3 years younger .009

(.009)Full siblings .009

(.004)

Stepsiblings .026

(.033)

Half siblings .032**

(.008)

Adopted and foster siblings .030

(.022)

Socioeconomic status .046**

(.005)

.045**

(.005)

.046**

(.005)

.045**

(.005)

Parents age .001(.000)

.001(.000)

.001(.000)

.001(.000)

Child has disability (vs. does not) .161**

(.013)

.156**

(.013)

.157**

(.013)

.154**

(.013)

Childs age .005**

(.001)

.006**

(.001)

.006**

(.001)

.006**

(.001)

Child in center care (vs. not) .111**

(.012)

.103**

(.012)

.103**

(.012)

.102**

(.012)

Childs health .035**

(.006)

.034**

(.006)

.034**

(.006)

.033**

(.006)

Birth weight .004

(.004)

.005

(.004)

.005

(.004)

.006

(.004)Lives with both biological parents

(vs. all other family types)

.114**

(.012)

.126**

(.012)

.126**

(.012)

.112**

(.012)



11/18

(For further information, see U.S. Department ofEducation, 2000.) Further, given the statisticalpower of over 20,000 cases, we rejected the nullhypothesis only when coefficients were significantat the .01 level or below in two-tailed tests.

RESULTS

Number of Siblings and Cognitive Skills

Table 2 presents the results of unadjusted andadjusted models predicting childrens reading andmath test scores. The unadjusted model suggeststhat children benefit by having one versus no sib-lings in terms of math skills (b .884; p< .001).Consistent with past research, however, this limitedadvantage appears to be a function of importantdifferences between the kinds of families with oneversus two children because the effect is no longersignificant in the adjusted model. Indeed, like the

bulk of past research, once we statistically adjustthe models to account for differences in familystructure, socioeconomic status, and other back-ground characteristics, our models reveal no cog-nitive skill advantage to having even onesibling. When the focus is on slightly largersibships (e.g., children with two, three, or fouror more siblings), the effects are consistentlynegative. Again, consistent with past work,children with zero or one sibling(s) outperformtheir counterparts with two or more siblings on

both math and reading standardized tests. Insome cases, the magnitude of the effect of liv-ing in a small versus large family is note-worthy. For example, the difference between

having four or more versus zero siblings forreading tests scores is comparable to movingup 2 points on the 5-point SES scale.

Number of Siblings and Social Skills

Our main question is whether we can locate anadvantage to having siblings when the focus is onchildrens social and interpersonal skills. Table 3

presents the results of models predicting teachersratings of kindergartners interpersonal skills.Model 1 suggests that teachers rate children withone sibling (b .112; p< .001), two siblings(b .120; p< .001), and three siblings (b .074;

p< .001) as having better interpersonal skills thanthose with no siblings. These differences arereduced by roughly 50% in the adjusted Model 2,but the coefficients for one sibling and two siblingsare still statistically significant, consistent with thehypothesis that childrens interpersonal skills are

improved as a result of exposure to one or twoversus no siblings at home. Decomposing sibshipsize into number of brothers and number of sisters,or older and younger siblings, reveals no statisti-cally significant patterns, but we do see evidencethat full siblings promote interpersonal skillswhereas half siblings do not (Model 5).

In Table 4, we see that teachers also rate childrenwith siblings as exhibiting fewer externalizingproblem behaviors than only children. In Model 1,children with any number of siblings are rated better

than only children (negative coefficients representfewer problem behaviors), and this time, the effectspersist even in the adjusted models. Differencesbetween brothers and sisters are negligible, and

TABLE 3. CONTINUED

Interpersonal Skills


Black (vs. White) .138*(.016)

.140*(.016)

.141*(.016)

.142*(.016)

Hispanic (vs. White) .020

(.016)

.022

(.016)

.022

(.016)

.022

(.016)

Asian (vs. White) .039

(.021)

.031

(.021)

.031

(.021)

.029

(.021)


(.022)

.057

(.022)

.056

(.022)

.055

(.022)

Constant 2.25 2.37 2.44 2.44 2.46





12/18

TABLE 4

RESTRICTED MAXIMUM LIKELIHOOD ESTIMATES OF CHILDRENS EXTERNALIZING PROBLEM BEHAVIORS (N 20,649)

Externalizing Problem Behaviors



(.012)

.095**

(.012)


(.013)

.117**

(.013)


(.018)

.115**

(.024)

Four or more siblings (vs. none) .170**

(.024)

.115**

(.024)

Number of brothers .019**

(.006)

Number of sisters .023**(.005)

Siblings! 3 years older .016*

(.006)

Siblings 12 years older .035*

(.010)

Siblings within 1 year .038*

(.011)

Siblings 12 years younger .050**

(.012)


(.008)Full siblings .034**

(.004)

Stepsiblings .003

(.030)

Half siblings .017

(.008)


(.016)


(.004)

.025**

(.004)

.025**

(.004)

.025**

(.004)


.001(.000)

.001(.000)

.001(.000)


(.013)

.121**

(.013)

.122**

(.013)

.119**

(.013)

Childs age .002

(.001)

.002

(.001)

.002

(.001)

.002

(.001)


(.013)

.183**

(.013)

.183**

(.013)

.182**

(.013)

Childs health .018*

(.006)

.018*

(.006)

.019*

(.006)

.018*

(.006)

Birth weight .006

(.004)

.006

(.004)

.006

(.004)

.007


(.012)

.152**

(.012)

.152**

(.012)

.133**

(.012)



13/18

there is only modest evidence that birth order andspacing matter, with children benefiting the leastfrom siblings 3 or more years younger. Similar tothe results for interpersonal skills, full siblings areassociated with better evaluations (b.034;

p< .001), whereas half and stepsiblings are not.Having siblings versus not having any is also

associated with better teacher evaluations of self-

control (Table 5). Children with siblingsanynumberare rated as exhibiting more self-control than only children, a pattern that persistsin adjusted models. Children do not appear togain this skill any more from sisters versus broth-ers, however, and the effects for birth order andspacing are modest but hint at more closelyspaced siblings as promoting self-control betterthan those widely spaced. Finally, full siblingsonce again promote social skills (b .020;

p< .001) but other kinds of siblings do not.

In sum, we see consistent evidence that chil-dren are rated as exhibiting better social andinterpersonal skills when they have at least onesibling. Recall that the apparent cognitive benefitof having one versus no siblings disappears whenwe control for differences between the kinds offamilies producing different numbers of children(Table 2). In contrast, when our models predict-ing social skills are subjected to the same statis-tical controls, the benefit of having siblingspersists. There is also moderate evidence that

full siblings promote childrens social skillsmore so than other types of siblings. This patternmay reflect a real benefit of interacting with fullsiblings compared to other types of siblings, or it

may reflect differences (not measured in ourmodels) between children with full and othertypes of siblings. As one example, children withother types of siblings may experience more resi-dential moves than children with full siblings as aresult of changes in family structure. To the extentthat moves cause familial stress, the lower levelsof social skills observed among children with

other types of siblings may reflect this additionalfamilial stress rather than actual lower qualitysibling relationships.

In supplemental analyses (not shown), wetested whether only children in (a) socioeconom-ically advantaged families and in (b) biologicalmother and father households are less susceptibleto exhibiting poor social skills than their counter-parts in poor households and those lacking one orboth biological parents. Models with interactions(sibship size*socioeconomic status and sibship

size*mother and father household status) suggestthat only childrens generally poorer social skillsare evident in high-SES and mother and fatherhouseholds too. Overall, these patterns suggestthat the consequences of sibship size for chil-drens social skills do not vary in importantways across subgroups (e.g., socioeconomic sta-tus, family structure). The benefit of having anadditional sibling appears roughly similar for allgroups. We also considered the effect of brothersversus sisters in models restricted to comparisons

between children with zero and one sibling(s) sothat our gender composition variable was notconfounded with sibship size. These results sug-gested that when children have just one sibling,

TABLE 4. CONTINUED

Externalizing Problem Behaviors


Black (vs. White) .155**(.017)

.156**(.017)

.156**(.017)

.159**(.017)


(.014)

.010

(.014)

.011

(.014)

.010

(.014)

Asian (vs. White) .140**

(.020)

.128**

(.020)

.128**

(.020)

.123**

(.020)

Other race (vs. White) .061*

(.022)

.065*

(.022)

.064*

(.022)

.062*

(.022)

Constant 2.11 2.05 1.99 2.00 1.97





14/18

TABLE 5

RESTRICTED MAXIMUM LIKELIHOOD ESTIMATES OF CHILDRENS SELF-CONTROL (N 20,649)

Self-Control



(.012)

.079**

(.013)


(.013)

.088**

(.018)


(.017)

.081**

(.018)

Four or more siblings (vs. none) .114**

(.023)

.074*

(.025)

Number of brothers .007

(.006)

Number of sisters .011(.006)

Siblings! 3 years older .006

(.005)

Siblings 12 years older .026

(.010)

Siblings within 1 year .020

(.011)

Siblings 12 years younger .033*

(.011)


(.008)Full siblings .020**

(.005)

Stepsiblings .017

(.029)

Half siblings .022

(.009)


(.020)


(.004)

.031**

(.004)

.031**

(.004)

.031**

(.004)


.001(.000)

.001(.000)

.001(.000)


(.016)

.139**

(.016)

.140**

(.016)

.138**

(.016)

Childs age .005**

(.001)

.005**

(.001)

.005**

(.001)

.004**

(.001)


(.012)

.131**

(.012)

.130**

(.012)

.130**

(.012)

Childs health .020

(.008)

.020

(.008)

.020

(.008)

.019

(.008)

Birth weight .006

(.004)

.005

(.004)

.005

(.004)

.005


(.013)

.143**

(.013)

.142**

(.013)

.128**

(.013)



15/18

there is no social skills advantage to having asister versus a brother.

DISCUSSION

Although common sense suggests that childrenbenefit from having some brothers and sisters,until now, there has been very little empiricalsupport for this position (Blake et al., 1991;Polit & Falbo, 1987). Indeed, the consensus amongpast studies of the relationship between sibshipsize and social skills was that additional siblingshave no positive effect on social skills. As aresult, Blake (1981b) argued that the commonlyespoused prejudice against the only child wasunjustified. Our study improves upon past work

in several ways, however, and we come to adifferent conclusion. We find that children withsiblings exhibit better social and interpersonalskills, on average, than children without siblings.If childrens social skills improve as a result ofexposure to at least one sibling, the patterns weobserve here could cumulate over time so that thegap in social skills between only children andchildren with siblings would grow.

Although we consistently find more supportfor the siblings as resources view than the

resource dilution view, less clear is which sibshipsize is most conducive to the development ofsocial skills. Some of our patterns suggest thatthe main distinction is between children with zeroversus any siblings, consistent with the threshold

argument that children benefit from one siblingas much as several. The two dependent variablesfollowing this pattern (self-control and external-izing problem behaviors) primarily indicate theextent to which children can regulate negativeemotions (Fabes, Hanish, Martin, & Eisenberg,2002). Perhaps having siblings, even just one,more frequently puts children in positions inwhich they experience and are expected to con-trol these negative emotions.

For one of our dependent variables, however,the results indicate that the benefit of siblingsbegins to wane as sibship size increases.Teachers ratings of childrens interpersonal skills(e.g., forming and maintaining friendships, gettingalong with people who are different, showing sen-sitivity to the feelings of others) suggest thatchildren with one or two siblings are more skilledthan those with no siblings, but that additionalsiblings beyond two are no better than havingno siblings. Overall, these patterns are consistentwith the view that childrens social skills improvewhen they have at least one sibling but that thisbenefit declines when sibship size grows to threeor more. If this relationship is causal, it mayrepresent childrens greater opportunities forparent-supervised sibling interactions in smallsibships versus large sibships or families with

only one child.In analyzing whether some types of siblingsaffect social skills differently from others, wefind little support for the position that childrenbenefit more from sisters than brothers, and only

TABLE 5. CONTINUED

Self-Control


Black (vs. White) .162**(.018)

.165**(.018)

.165**(.018)

.166**(.018)


(.014)

.007

(.018)

.007

(.014)

.007

(.018)

Asian (vs. White) .093**

(.019)

.086**

(.019)

.086**

(.021)

.082**

(.019)


(.022)

.051

(.022)

.050

(.022)

.048

(.022)

Constant 2.44 2.54 2.62 2.61 2.64





16/18

modest evidence that closely spaced siblings(presumably providing greater opportunities forinteraction) promote social skills more thanwidely spaced siblings. Our most consistent evi-dence, in terms of the kinds of siblings that mat-ter, is that children benefit more from exposure to

full siblings than other kinds of siblings.This study represents the first attempt (that we

are aware of) to study the relationship betweennumber of siblings and social skills using third-party ratings in nationally representative data.Although our results provide a basis for futurework, the ways in which our conclusions aretempered should not be overlooked. First,although these results are the first to suggest aconsistent social skills advantage for childrenwith siblings, the size of the siblings effect ismodest. Sibship size effects are typically ofgreater consequence, sometimes of much greaterconsequence, for social skill development thanmoving up one unit on a 5-point SES scale, butthey are still not large. Based on these results, wewould hesitate to encourage parents of only chil-dren to have another child as a strategy for devel-oping their existing childs social skills.

Second, we maintained a focus on sibship sizeand other structural components of sibship, butour results raise several questions about the pro-cesses occurring within families that shape socialskills. At the aggregate level, teachers rate chil-dren with one sibling as more socially skilledthan children with no siblings, but we wouldlearn more about why siblings are associatedwith better social skills if we studied the pro-cesses within families and between siblings thatpromote social skill development. To date, thiskind of work suggests that some sibling relation-ships (e.g., those characterized by warmth andengagement) are better than others (Brody,1998; Dunn, Slomkowski, Beardsall, & Rende,1994). Further work along these lines might iden-tify conditions (e.g., chronically high-conflictsibling relationships) under which an additionalsibling is not an advantage over only-child status.

Third, measuring childrens social skills per-suasively remains a challenge. We used scalesconstructed from multiple questions asked ofteachers. We were interested in teacher evalu-ations because we wanted to test whether siblings

at home would be associated with social skillsexhibited elsewhere, such as the classroom. Insupplemental analyses, we considered how parentevaluations of social skills were related to sibshipsize. In some cases (e.g., externalizing problem

behaviors), the patterns replicate what wereported here, based on teacher evaluations. Inother cases (e.g., interpersonal skills), the pat-terns were different; parents of only childrengave ratings of their children that were moresimilar to those of parents of children with one

or two siblings, and better than those of parentswith children who have three or more siblings.These discrepancies, perhaps a result of parentsemphasizing at-home interactions while teachersrated at-school interactions, merit further investi-gation.

Fourth, our models more rigorously controlledfor differences between families of varying sib-ship size than past studies, but we still cannotdismiss the possibility that the patterns weobserve here merely reflect a spurious relation-ship between sibship size and social skills. Thereare probably differences, unaccounted for in ourmodels, between families with one versus morethan one child; our pattern of results could reflectthese unmeasured differences rather than any realbenefit of siblings. What might these unobservedcharacteristics be? One possibility is that parentsfertility decisions are shaped in part by the tem-perament of their current children. If, for exam-ple, parents with a difficult child stop at one birthmore frequently than parents of amiable children,our pattern of results may not reflect a socialskills benefit to sibling exposure, but tempera-mental differences between childrendiffer-ences that shaped the number of children theirparents wanted. In our study, these variations intemperament are probably gauged in part by ourindicators of childrens birth weight, health, anddisability status, but these are surely imperfectmeasures. Another possibility is that parentswith only one child are, on average, less socially

skilled than their counterparts who have two chil-dren. If this is the case, children with a siblingmight exhibit greater social skills than thosewithout a sibling because of skills learned fromtheir parents, not their siblings.

Resolving these issues with nonexperimental datais a challenge, but one possibility is to use gain orsibling resemblance models. In supplemental ana-lyses, for example, we found that children in theECLS-K who gained a sibling between the begin-ning of kindergarten and the end of first grade did

not gain more social skills than their counterpartswho did not gain a sibling, evidence consistent withthe spurious explanation. But because past researchsuggests that children exhibit poorer social skillsduring the first 2 years after a new sibling is born



17/18

(Baydar et al., 1997), these results offer little help.The less-than-2-year interval between the first andlast wave of available ECLS-K data is too short toexpect an observable social skills benefit fromadding such young siblings. Future waves ofECLS-K data may make this test more reasonable,

but even then the tests will only assess the effectsof a particular kind of sibling (e.g., widely spacedyounger siblings). Researchers have also employedsibling resemblance models, but they requireat least one sibling and thus would be inappro-priate for assessing the main finding in this study:that there are social skills differences between chil-dren with zero and one or more siblings.

Despite these persistent concerns, the resultsfrom this study make a compelling case for theposition that children hone social and interper-sonal skills through sibling interactions at home,and that these skills then become useful outsidethe home. In the last four decades, the averagenumber of children ever born to Americanwomen has been nearly cut in half, and yet theconsequences of this important demographic shiftare not well understood. On average, childrenmay receive more parental resources (Downey,1995) and more help paying for college now thanin the past (Steelman & Powell, 1989). But ourstudy suggests that the generally good newsaccompanying lower fertility has at least onedownside: When it comes to learning how toget along with peers, children may miss out inimportant ways by not having at least one sibling.

NOTE

The authors appreciate the helpful comments and sugges-tions of Brian Powell, Lisa N. Hickman, and Maureen

Tobin.

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the benefit of siblings at home

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