Occupational and Environmental Medicine 1996;53:351-356

Psychosocial and physical risk factors formusculoskeletal disorders of the neck, shoulders,and lower back in salespeople

Torsten Skov, Vilhelm Borg, Elsa 0rhede

AbstractObjectives-To analyse the associationbetween symptoms from the muscu-loskeletal system and many psychosocialand other physical stressors in the jobdemand-control-support model. Also toanalyse the influence of personality char-acteristics.Methods-1306 salespeople answered aself administered questionnaire on jobcharacteristics, exposures, personalitycharacteristics, social network, smokingand drinking habits, and symptoms of theneck, shoulders, and low back.Results-In multivariate analyses, highjob demands were related to neck andshoulder symptoms (ORs 1-43-1-47 in thehighest exposure groups compared withthe lowest), and tendency to become over-worked and lack of social support fromcolleagues were related to back pain (OR1*81-2*04 in the highest exposure groupscompared with the lowest). Lack of varia-tion in the job, low control over time, andhigh competition were related to necksymptoms, but there was an interactionso that both low control over time andhigh competition had to be present toincrease the OR. Also, driving long dis-tances and sedentary work were related toneck and low back pain, and time spent inthe car to shoulder pain (ORs 1-64-2*80 inthe three highest groups v the lowestexposure groups).Conclusion-Both psychosocial and phys-ical factors were associated with muscu-loskeletal symptoms. Many dimensions ofthe demand-control-support model wereassociated with symptoms. Only one per-sonality characteristic, tendency to feeloverworked, significantly influenced theprevalence ofmusculoskeletal symptoms.

(Occup Environ Med 1996;53:351-356)

National Institute ofOccupational Health,Lerso Parkalle 105,DK-2100 Kobenhavn0, DenmarkT SkovV BorgE 0rhedeCorrespondence to:Dr Torsten Skov, NationalInstitute of OccupationalHealth, Lers0 Parkalle 105,DK-2100 Kobenhavn 0,Denmark.

Accepted 15 December 1995

Keywords: decision latitude; job demand-control-support model; driver; sedentary work

For reasons only partly understood, muscu-loskeletal disorders have become increasinglycommon in western countries during the pastdecades. Physical loads such as repetitiveheavy lifing especially in twisted positions,and motor vehicle driving are established riskfactors for back pain.' Sustained static loadand repetitiveness are established risk factorsfor neck and shoulder disorders.2

During the past few years the contributionof psychosocial stressors to the occurrence ofmusculoskeletal disorders has become increas-ingly clear. The job demand-control-supportmodel, which has been widely used as a modelfor relations between the psychosocial workenvironment and cardiovascular disease, hasalso been introduced in studies of muscu-loskeletal disorders. A recent review of publi-cations on psychosocial factors at work andmusculoskeletal disease4 concluded that highjob demands have consistently been associatedwith musculoskeletal symptoms. Furthermore,the data indicated that lack of control and lackof social support at work are positively associ-ated with musculoskeletal disorders.

In most studies only one or a few psychoso-cial factors have been taken into accountsimultaneously. Bongers et a!4 noted that nostudies existed of back trouble which analysedthe effect of demands, control, and social sup-port at the same time. It was also noted thatseveral studies did not control appropriatelyfor physical load. As high psychosocial jobdemands are often correlated with high physicalload, it could be argued that the associationsfound for the psychosocial factors were due toresidual confounding from the physical fac-tors.

In a population based study of patients whoconsulted a physician for neck and shoulderdisorders, the work organisation and the psy-chosocial work conditions were as importantdeterminants for disease as were the physicalwork conditions.5 Similar findings werereported in a group of newspaper workers,6and a study of a population sample fromHolland.7A person's way of coping with a potential

stressor in the work environment could deter-mine whether or not the stressor will have anadverse effect.8 Evidence of such effect modifi-cation is missing for musculoskeletal disor-ders, but some studies have suggested anassociation between type A behaviour andneck, shoulder, and low back pain.4 9We did a study among salespeople. Many

salespeople experience high job demands andcompetition with other salespeople. Theywork outside the company in which they areemployed, and have little contact with col-leagues. On the other hand, many salespeoplehave a high degree of control over and varia-tion in the job. The physical exposures in thejob include prolonged driving, sedentary work,and among some subgroups lifting of heavyloads. Thus, salespeople are a suitable groupfor estimating the effects of a range of psy-

351

on Decem

ber 24, 2021 by guest. Protected by copyright.

http://oem.bm

j.com/

Occup E

nviron Med: first published as 10.1136/oem

.53.5.351 on 1 May 1996. D

ownloaded from

Skov, Borg, 0rhede

chosocial and physical exposures, each con-trolled for the possible confounding effects ofthe others.The primary objective of the study was to

test the variables of the job demands-control-support model, including possible modifica-tion of effect (interaction) between demandsand control.A secondary objective was to test whether

personality characteristics modified the associ-ations between psychosocial stressors at workand musculoskeletal symptoms.Many other variables were included in the

analyses, mainly to obtain unconfoundedresults for above mentioned objectives. Thesewere, for example, social network in privatelife, uncertainty of employment prospects, andwork role. Also physical exposures such as lift-ing, sitting, and driving long distances wereincluded.

Material and methodsA questionnaire was posted to a random 8%sample of the members of the associationDanish Active Salespeople. The 1991 ques-tionnaires were sent, and 1306 (66%) werereturned completed. Of the salespeople 3%declined to participate, 3% returned a blankquestionnaire, 3% said that they were unem-ployed or no longer salespeople, and 25% didnot respond at all.

DEFINITION OF OUTCOMEMusculoskeletal symptoms were ascertainedwith the Nordic questionnaire on muscu-loskeletal disorders supplemented with a ques-tion on the intensity of symptoms on a 10point scale ranging from none to very, veryintense.'0 For the present analyses outcomeswere defined as symptoms (tenderness, pain,discomfort) during the past 12 months fromthe body region in question (neck, shoulders,low back). People who reported trauma to thegiven body region were excluded. Preliminaryanalyses showed that the symptom intensitywas not associated with the exposure intensity.Therefore the symptom intensity was notincluded in the definition of the outcome.

EXPOSURESQuestions were asked about the annual drivingdistance, time in sedentary work, car equip-ment and price, and lifting of heavy loads.Leisure time sports activities were also ascer-tained.The psychosocial job characteristics were

assessed with questions on demands, control,and social support" 12 supplemented withquestions on perceived competition fromother salespeople developed for this study, roleconflict,'3 and uncertainty of employment

Table 1 Age and prevalences ofsymptoms in the past 12 months

Agemean Neck Shoulders Low back

n (SD) % % %

Men 1167 42-0 (9-9) 54 35 63Women 137 36-5 (7-8) 76 47 64

prospects. '4 A factor analysis (discussed later)identified 11 factors.The first two were concerned with the

demand part of the demand-control-supportmodel:-job demands (especially items like highdemands for concentration and speed in thework)

-perception of competition (with salespeoplefrom other companies).Two other factors were concerned with the

control part of the demand-control-supportmodel:-control over the content of the job-control over time aspects of the work (items

like deciding working hours, holidays).Two factors were concerned with the sup-

port part of the demand-control-supportmodel:-social contact and support from colleagues-support from superiors.

Five factors were concerned with otheraspects of the psychosocial work environment:-uncertainty of employment prospects (being

concerned that one may become unem-ployed, transferred to another job, etc)

-conflicts with colleagues-work role ambiguity (unclearly defineddemands in the work)

-work role conflict (conflicting demands inthe work)

-variation in the work.The social network outside the job was

assessed with questions originally developedfor the Alameda study, in the Nordic coun-tries.'5 The factors concerning social networkwere:-contact with the social network-influence on people in the social network-feeling accepted by people in the social net-work

-feeling close to people in the social network-feeling that one is part of a larger social net-

work.Personality characteristics were assessed

with questions obtained from J Siegrist andtranslated into Danish.'6 These were:-tendency to become overworked-confronting attitude toward other people-individualistic attitude-tendency to be late-ambitious attitude-acceptance seeking-sensitive to interruptions.

Finally, other variables used in the analysisincluded sex, type of product sold, weeklyworking hours, time spent with customers,number of nights spent away from the home,type of wage earning system, smoking (passiveand active), weight, height, and age.

STATISTICAL ANALYSESFactor analysis was used. Varimax rotationwas used to find the most obvious factors.Variables with factor loadings above 0 40 wereincluded in the factors. Responses weresummed to form a joint score on each factor.The scores were grouped into empirical quar-tiles which were used in the tabulations as wellas regressions. For control over time and per-

352

on Decem

ber 24, 2021 by guest. Protected by copyright.

http://oem.bm

j.com/

Occup E

nviron Med: first published as 10.1136/oem

.53.5.351 on 1 May 1996. D

ownloaded from

Psychosocial andphysical risk factors for musculoskeletal disorders of the neck, shoulders, and lower back in salespeople

Table 2 Symptoms of the neck during the past 12 months (final main effects model)

P value forlogistic

Factors: variables OR (95% CI) regression PPR (95% CI)

Sex: 0.000Men 1 1Women 2-76 (1-72-4-43) 1-39 (1 10-1-75)

Annual driving distance (kin): 0 011<5000 1 15-10 000 0.99 (0-45-2 2) 0-99 (0-55-1-76)10-15 000 1-48 (0-75-2 93) 1-20 (0-74-1-92)15-30 000 1-74 (1-01-299) 1-29 (0-88-1-89)30-50 000 2-10 (1-24-3-54) 1-39 (0-96-2-00)> 50 000 2-43 (1-36-4-34) 1-46 (0 99-2 17)

Sedentary work (proportion ofwork time): 0-018None or infrequently 1 1

2-68 (1-31-5-49) 1-62 (0-95-2 75)1-92 (098-3-79) 1-42 (085-2 37)2-18 (1 11-4-29) 1-49 (0-89-2 48)

All 2-80 (1 40-5-59) 1-64 (0-98-2-75)Demands in the work (quartiles): 0 033

Lowest 1 1Nexttolowest 0-84 (06-1-19) 092 (0-73-1-16)Nextto highest 1-13 (0-8-1-59) 1-05 (0-84-1-31)Highest 1-43 (0 99-2 06) 1 14 (0 91-1 43)

Variation in the work (quartiles): 0 010Highest 1 1Next to highest 1-78 (1-16-2-73) 1-30 (0-98-1-73)Nextto lowest 1-36 (0-95-1-96) 1-16 (0-90-1 50)Lowest 1-82 (1-23-2-69) 1-31 (1 01-1 70)

Control over time (quartiles): 0-046High (top two quartiles) 1 1Medium 1 09 (0-8-1-5) 1-04 (0-84-1-29)Low 1-44 (1-07-1-93) 1-15 (0-96-1-39)

Perceived competition (quartiles): 0-033Low 1 1Medium 1-38 (0-98-1-93) 1-15 (0-92-1-43)High (top two quartiles) 1-44 (1 08-1 91) 1-16 (0-96-1 40)

Table 3 Neck symptoms during the past 12 months (ORs (95% CIs) for the interactingvariables control over time and perceived competition from other salesmen: P value for theinteraction = 0-016)

Control over time

High Low

Perceived competition fromother salesmen:High 1-16 (0-68-2 00) 1-85 (1-32-2-60)Low 1-20 (0-78-1-85) 1 (reference)

Interacting variables dichotomised, all other variables entered into the model as in table 2.

Table 4 Final modelfor symptoms from the shoulders during the past 12 months

P valueforlogistic

Factors: variables OR (95% CI) regression PPR (95% CI)

Sex: 0 004Men 1 1Women 1-77 (1 20-2 62) 1-38 (1-04-1-84)

Time spent in the car a week (h): 0-024< 10 1 110-19 1 64 (1-19-227) 1-36 (1-06-1-79)20-29 1-39 (095-203) 1-25 (092-1-69), 30 1-64 (099-2-7) 1-38 (092-2-01)

Smoking: 0-045Non-smoker 1 1Exsmoker 1 22 (0 87-1 70) 1 15 (0 88-1 50)Smoker 1 46 (1-08-1-96) 1-27 (1 00-1 60)

Demands in the work (quartiles): 0 034Lowest 1 1Next to lowest 0.91 (0-64-1-29) 0-94 (0-71-1-24)Next to highest 1-07 (0-76-1-51) 1-04 (0-79-1-37)Highest 1-47 (1-05-2-07) 1-25 (0 96-1-62)

Uncertainty of employmentprospects (quartiles): 0-006Lowest 1 1Nextto lowest 1-20 (0-89-1 63) 1-13 (0-89-1-44)Next to highest 1-76 (1-262-46) 1-40 (1-09-1-80)Highest 1-52 (1 01-2 29) 1-30 (0-95-1-77)

Risk estimates are also controlled for age.

ceived competition three groups were usedinstead of four because the highest score valuewas very prevalent.P values for cross tabulations were calcu-

lated from X2 statistics. Unconditional logisticregression models were fitted with proc probitin SAS, starting with models including all vari-ables which were significant or nearly signifi-

cant (P < 0 10) in the bivariate tabulations.Variables were successively deleted from themodels based on the magnitude of the Waldtest x2 based statistic and considerations as tothe scientific relevance of the variable. Age wasnot significant in any of the models but waskept in the final model for shoulder symptomsbecause some of the other risk estimateschanged more than 10% when age wasincluded. Interaction terms between the psy-chosocial variables that were significant in thefinal main effects model were tested, but wereonly kept if significant (one of them was).

For each of the final main effects logisticregression models an equivalent Cox's regres-sion model was fitted.'7

Factor analyses were done in SPSS, allother analyses were done in SAS.

ResultsTable 1 shows the sex and mean age of thestudy population, and the overall prevalencesof symptoms during the past 12 months inneck, shoulders, and low back.

NECKTable 2 shows the risk estimates from the finalmain effects model for neck symptoms.Women had an increased risk of neck symp-toms during the previous 12 months com-pared with men. The risk estimates increasedmonotonically with increasing annual drivingdistance. Having sedentary work for morethan a quarter of the work time was associatedwith an odds ratio (OR) for neck symptoms of1-9 or more. The risk estimates increasedmonotonically or almost monotonically withincreasing demands, decreasing control overthe time of the work, and increasing competi-tion with other salespeople. A large amount ofperceived variation in the work was protectivewhereas the lower three quartiles had aboutthe same risk estimates (ORs 1 36-1 82).

There was an interaction between controlover time and perceived competition fromother salespeople (P = 0-016), in that onlythe combination of low control and high com-petition was associated with an increased riskof neck symptoms (table 3). For the othercombinations of control and competition theORs were close to unity.

SHOULDERSWomen had a greater prevalence of shouldersymptoms during the previous 12 months thanmen (table 4). Spending more than 10 hours aweek in the car was associated with ORs forshoulder symptoms of 1-39 or more. Smokersand exsmokers had increased risks. Those withthe highest job demands had significantlyhigher risk estimates than the lower threequartiles. Finally, the perception of uncertainemployment prospects was associated withincreased symptoms.

LOW BACKThe risk estimates for low back symptomsincreased monotonically with increasingannual driving distances over 10 000 kilome-

353

on Decem

ber 24, 2021 by guest. Protected by copyright.

http://oem.bm

j.com/

Occup E

nviron Med: first published as 10.1136/oem

.53.5.351 on 1 May 1996. D

ownloaded from

Skov, Borg, 0rhede

Table 5 Final modelfor symptomsfrom the low back during the past 12 months

P value forlogistic

Factors: variables OR (95% CI) regression PPR (95% CI)Annual driving distance (km): 0-022<5000 1 15-10 000 1-40 (0-65-3 04) 1-18 (0 68-2 04)10-15 000 1-89 (0 96-3-73) 1-35 (0-842-16)15-30 000 2-23 (1-29-3-85) 1-44 (0-982-12)30-50 000 2-18 (1-28-3-72) 1-43 (0 98-209)> 50 000 2-79 (1-54-5-07) 1-54 (1-03-2-30)

Sedentary work (proportion ofwork time): 0 053None orinfrequently 1 1

1-70 (0-84-344) 1-25 (0 78-2 04)1-63 (0-84-3-18) 1-25 (0-78-1-98)

i 1-78 (0-91-3 46) 1-28 (0-81-2-03)All 2-45 (1-24-4-85) 1-42 (0-89-2-26)

Smoking: 0-036Non-smoker 1 1Exsmoker 1-51 (1-09-2-10) 1-16 (0-96-1-41)Smoker 1-31 (0-98-1-76) 1 11 (0-93-1-32)

Social contact with colleagues(quartiles): 0 019Most 1 1Nexttomost 1-40 (099-1-98) 1-15 (0-92-1-43)Next to least 1-48 (1-03-2-14) 1-17 (0-93-1-46)Least 1-81 (1-25-2-63) 1-24 (0 99-1 55)

Tendency to feel overworked(quartiles): 0 001Least 1 1Nexttoleast 1 11 (0-80-1-56) 1-05 (0-85-1-30)Next to most 1-45 (1-06-1-98) 1-15 (0-95-1-39)Most 2-04 (1-39-3-00) 1-27 (1-02-1-57)

Risk estimates are also controlled for personal height.

Table 6 Summary offindings by body region

Neck Shoulders Low back

Factors significant in final models:Sex + +Driving distance + +Sedentary work + +Time spent in the car +Demands in the work + +Variation in the work +Control over time +Perceived competition +Smoking + +Uncertain employment prospects +Social contact with colleagues +Tendency to feel overworked +Height +

Factors not significant in final models:Car equipmentCar priceLifting heavy loadsLeisure time sport activitiesNumber of nights spent away from homeType of wage systemType of product soldAgeWeightControl over content of the workSupport from superiorsWork role ambiguityWork role conflictSocial network (all dimensions)Confronting, individualistic, and ambitious attitudesTendency to be lateAcceptance seekingSensitivity to interruptions

tres (table 5). Having sedentary work for morethan a quarter of the work time was associatedwith ORs of 1-6 or more, and the riskincreased almost monotonically with increas-ing duration of sedentary work. Smokers andexsmokers were at increased risk. Monotonicincreases in the risk estimates were found withdecreasing social contact with colleagues andincreasing tendency to feel overworked.The risk estimates for back symptoms

increased monotonically with increasing bodyheight (not shown in the table). There was noassociation between sex and back symptoms.

Table 6 summarises the findings acrossbody regions.

DiscussionDemands in the work were significantly associ-ated with neck and shoulder symptoms (table6). High competition, lack of control overtime, and lack of variation, were significantlyassociated with neck symptoms, whereasuncertainty of employment prospects was sig-nificantly associated with shoulder symptoms,and lack of social support from colleagues andthe tendency to feel overworked were signifi-cantly associated with back symptoms. Longdriving distances and much sedentary work orlong periods spent in the car were associatedwith neck, shoulder, and low back symptoms.All estimates associated with particular vari-ables were adjusted for the effect of all othervariables that were in the model.

Residual confounding has been suggested asan explanation for the relation betweendemands and musculoskeletal disorders.4 It isargued that as high psychosocial job demandsare often correlated with high physical load,the associations might be due to lack of preci-sion in the assessment of the physical load. Inthe present study, apart from driving andsedentary work, the population had little phys-ical load: few salespeople (5%) lifted morethan 400 kg a day, and none had physicallyrepetitive work. Therefore the likelihood ofresidual confounding should be low.

Reporting bias has also been suggested asan explanation for the relation between jobstrain and health outcomes in cross sectionalstudies. It is argued that people who do notfeel well will tend to report more exposuresthan those who have no symptoms, partlybecause they perceive their work as stressfulbecause of their symptoms. In the presentstudy validation of self reports by observationwas not possible. However, the analysesincluded several questions which were proba-bly robust to reporting bias-for example, thenumber of kilometres driven per year.The questions on number of customer vis-

its, time spent with customers, etc, are probablyalso robust to reporting bias. They could havebeen used to assess the psychosocial expo-sures, but they would only have been proxiesfor the perceived work strain that we wantedto assess.A strong argument against the presence of

reporting bias in this study is the fact that theintensity of the symptoms was not related tothe degree of reported job stressors. If therewere reporting bias we would expect it to showup in a dose-response manner.A main weakness in this and most other

studies of musculoskeletal disorders dependson the definition of the outcome. In the strictsense, we assessed the probability of havingexperienced discomfort or pain in each bodyregion at least once during the past year. Most ofthe positive responses are due to mild and tran-sient discomfort which may or may not predictmore severe long term disease. Previous muscu-loskeletal disorders have been found to be riskfactors for present disorders. It is not clear,however, whether the risk estimates for symp-toms reflect the risks of-for example, longterm sick leave or early retirement.

354 on D

ecember 24, 2021 by guest. P

rotected by copyright.http://oem

.bmj.com

/O

ccup Environ M

ed: first published as 10.1136/oem.53.5.351 on 1 M

ay 1996. Dow

nloaded from

Psychosocial and physical risk factors for musculoskeletal disorders of the neck, shoulders, and lower back in salespeople

It has recently been debated whether preva-lence data should be analysed with logisticregression yielding ORs or with Cox's regres-sion yielding prevalence (proportion) ratios(PPRs). 19 If, in the present context, it isthought that the outcome to be assessed is therisk of experiencing some outcome (here oneepisode of pain or discomfort) at least onceduring a period of time (here 12 months), thenthis cumulative incidence is estimated directlyby the prevalence proportion, and the relevantmeasure of the relative risk is the PPR. As theprevalence of the outcome increases, then theOR tends to be an increasingly poor estimateof the relative risk.

If it is thought that the duration of disease isequal in the exposed and the unexposedgroup, then in a cross sectional study theprevalence odds ratio (POR) is equal to theratio of the incidences in the two groups,20 andthis is usually taken as a good measure of therelative risk. In our case, if the question onsymptoms shows the presence of a diseasewith a defined but unknown duration, which isthe same in the exposed and the unexposedgroups, then the OR is the relevant measure ofthe relative risk.

It may make sense to assume that the pres-ence during the past 12 months of muscu-loskeletal symptoms is indicative of someabnormality of the musculoskeletal system,but it is doubtful whether this definition wouldbe compatible with having a well defined dura-tion. Some authors argue that for muscu-loskeletal disorders the assumption of similarduration among exposed and unexposed sub-jects is in general doubtful.'8 For convenience,and as this is still the usual way to analyse thistype of data, we present an analysis based onlogistic regression. However, we also presentthe relative risks estimated as PRs analysedwith Cox's regression.17

JOB DEMAND-CONTROL-SUPPORT MODELThe factors perceived competition and lowvariation in the work were significantly associ-ated with neck symptoms, as was demand inthe work, which was also associated withshoulder symptoms. These findings, and theassociation between low control and necksymptoms, are consistent with previous stud-ies.4 We hypothesised that there might be aninteraction (effect modification) between jobdemands and job control. We found an inter-action between one work demand factor, per-ceived competition, and one control factor,control over time, so that only the combinationof low control and high demands was associ-ated with an increased prevalence of necksymptoms. One interpretation of these findingscould be that high job demands lead toincreased muscle tone, whereas control overtime makes it possible to distribute thedemands over the work time and thereby intro-duce rest periods that counteract ill effects.

Lack of social support only seemed to play apart for back disorders. Although one shouldnot over interpret this finding it seems to beconsistent with the scientific literature.4 Socialsupport from colleagues may entail direct help

with specific tasks, or indirectly may increasethe salesman's skills so that he can cope withthe job demands.

OTHER PSYCHOSOCIAL VARIABLESThe factor tendency to feel overworked wassignificantly associated with back symptoms.This was the only personality characteristicthat was significant in the analyses. One inter-pretation would be that people who have atendency to feel overworked have insufficientskills to manage their job demands.Alternatively, high demands could lead to afeeling of being overworked and thereby, indi-rectly, to symptoms. The hypotheses on inter-actions between personality characteristics andpsychosocial or physical work variables werenot substantiated. The relation between shoul-der symptoms and uncertain employmentprospects has not been reported before.

PHYSICAL FACTORSThe risk for neck and back symptoms was highamong those who drove long distances andthose who had much sedentary work. Bothfactors were significant after controlling for theother. Lifting was not significantly associatedwith symptoms, but this should not beregarded as evidence against a relation becausethere was little difference in loads liftedbetween salespeople.

In multivariate analyses both physical andpsychosocial factors were associated with mus-culoskeletal symptoms. It is recognised thatthe cross sectional study design may entailsources of bias. We have argued against therisk estimates being seriously over estimated,but a follow up design would solve this prob-lem more effectively.

1 RiihimAki H. Low-back pain, its origin and risk indicators.Scand _J Work Environ Health 1991;17:81-90.

2 Hagberg M, Wegman DH. Prevalence rates and odds ratiosof shoulder-neck diseases in different occupationalgroups. Br 7 Ind Med 1987;44:602-10.

3 Kristensen TS. The demand-control-support model:methodological challenges for future research. StressMedicine 1995;11:17-26.

4 Bongers PM, de Winter CR, Kompier MAJ, HildebrandtVH. Psychosocial factors at work and musculoskeletaldisease. ScandJl Work Environ Health 1993;19:297-312.

5 Ekberg K, Bjorkqvist B, Malm P, Bjerre-Kiely B, KarlssonM, Axelson 0. Case-control study of risk factors for dis-ease in the neck and shoulder area. Occup Environ Med1994;51:262-6.

6 Bernard B, Sauter S, Fine L, Petersen M, Hales T. Job taskand psychosocial risk factors for work-related muscu-loskeletal disorders among newspaper employees. ScandJ Work Environ Health 1994;20:417-26.

7 Houtman 1ID, Bongers PM, Smulders PGW, KompierMAJ. Psychosocial stressors at work and musculoskeletalproblems. ScandJ7 Work Environ Health 1994;20:139-45.

8 Cooper CL, Payne R, eds. Causes, coping and consequences ofstress at work. Chichester, New York, Brisbane, Toronto,Singapore: John Wiley, 1988.

9 Flodmark BT, Aase G. Musculoskeletal symptoms andtype A behaviour in blue collar workers. Br J Ind Med1992;49:683-7.

10 Kuorinka I, Jonsson B, Kilbom A, Vinterberg H, Biering-Sorensen F, Andersson G, Jorgensen K. StandardisedNordic questionnaires for the analysis of musculoskeletalsymptoms. Applied Ergonomics 1987;18:233-7.

11 Karasek RA. Job demands, job decision latitude, and men-tal strain: implications for job redesign. AdministrativeScience Quarterly 1979;24:285-308.

12 Marmot MG, Smith GD, Stansfeld S, Patel C, North F,Head J, et al. Health inequalities among British civil ser-vants: the Whitehall II study. Lancet 1991;337:1387-93.

13 Fisher CD, Gitelson R. A meta-analysis of the correlates ofrole conflict and ambiguity. J Appl Psychol 1983;68:320-33.

14 Nord-Larsen M, 0rhede E, Nielsen J, Burr H.Lonmodtagernes arbejdsmiljo 1990-bind 1. Sammenhaenge

355

on Decem

ber 24, 2021 by guest. Protected by copyright.

http://oem.bm

j.com/

Occup E

nviron Med: first published as 10.1136/oem

.53.5.351 on 1 May 1996. D

ownloaded from

Skov, Borg, Orhede

mellem arbejdsmilje og helbred. Kobenhavn:Arbejdsrniljofondet, 1992.

15 Ostergren P-0. Psychosocial resources and health: with specialreference to social network, social support and cardiovasculardisease. Malmo, Sweden: Department of CommunityHealth Sciences, Lund University, 1991.

16 Siegrist J, Peter R, Junge A, Cremer P, Seidel D. Low statuscontrol, high effort at work and ischemic heart disease:prospective evidence from blue-collar men. Soc Sci Med1990;31:1127-34.

17 Lee J. Odds ratio or relative risk for cross-sectional data? IntEpidemiol 1994;23:294.

18 Axelson 0, Fredriksson M, Ekberg K. Use of the preva-lence ratio v the prevalence odds ratio as a measure ofrisk in cross sectional studies. Occup Environ Med 1994;51:574.

19 Stromberg U. Prevalence odds ratio v prevalence ratio.Occup Environ Med 1994;51:143-4.

20 Freeman J, Hutchison GB. Prevalence, incidence and dura-tion. Am Epidemiol 1980;112:707-23.

Rejected manuscriptsFrom February 1994, authors whose sub- be returned to them. The 7ourmal will destroymitted articles are rejected will be advised of remaining copies of the article but corres-the decision and one copy of the article, pondence and reviewers' comments will betogether with any reviewers' comments, will kept.

356

on Decem

ber 24, 2021 by guest. Protected by copyright.

http://oem.bm

j.com/

Occup E

nviron Med: first published as 10.1136/oem

.53.5.351 on 1 May 1996. D

ownloaded from