developmental psychology: research issues intractable variables –difficult or impossible to...
TRANSCRIPT
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Developmental Psychology: Research Issues
• Intractable Variables– Difficult or impossible to manipulate
• Heredity/Genes• Environment• Age
– Age is a “proxy” for causal variables—i.e., age co-varies with these causal agents, but it is not a causal variable
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• Measurement Equivalence
– When constructs change with development, measures that are appropriate at one age (time) may be inappropriate at another age
• Ex: Assessment of attachment in preschoolers
– Is a separation-reunion procedure appropriate?
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• Self-report data are limited
– Parents, teachers, and other adults often complete “self-report” measures of children’s behavior
– Greater reliance on observational techniques
• Inferring the meaning of behavior is difficult
– Ex: Infants’ understanding of object permanence
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• Complexity of causal influences
– Ethical concerns preclude manipulation of many variables
• Ex: maltreatment and children’s development
– Laboratory analog studies may compromise external validity
• Ex: Marital conflict and children’s development
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• Direction of causation
– Biases/assumptions about the direction of influence
• Ex: parents influence children rather than the reverse
– Bidirectional influences are more likely than unidirectional influences
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General Research Designs
• Experimental Designs
– Manipulation of hypothesized independent variable
– Random assignment of participants to different conditions (between-subjects designs) OR other control procedures (within-subjects designs, small-n designs)
– Allow strong inferences about causal relationships
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• Potential Limitations of Experimental Designs
– Participant non-compliance in the “treatment” or “intervention” condition (e.g., dropping out, failure to participate fully in the treatment)
– Generalization (external validity)
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• Non-experimental (Correlational) Designs
– No manipulation of variables
– No random assignment or other comparable control procedures
– Not possible to make strong causal inferences
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Why not?
• Selection Bias (Confounding Variables)– Refers to third variables that are correlated
with both the predictor variable and the outcome variable
• Ex: Does high-quality child care cause improved school readiness?
– Children in high-quality child care (and their families) are likely to be different in many ways from children in lower-quality child care (socioeconomic status; high-quality parental care)
– These “confounding” variables are likely to be related to school readiness
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• Most common approach to reducing selection bias:
– Identify, measure, and control for possible confounding variables either in the research design or in the statistical analysis
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Developmental Designs
• Designs in which age-related change is examined
– Normative development (developmental functions)
– Individual differences
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Variables Involved in Developmental Designs
• Cohort: Groups of participants who are born or experience some other common event in the same time period
– Ex: children born in 1980 are a cohort; individuals growing up during the Great Depression are also a cohort
• Age
• Time/Point of Assessment
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Simple Developmental Designs
• Longitudinal Designs
– A single cohort is examined at multiple ages (and thus at multiple times of assessment)
– Age and time of assessment are confounded
• An event may occur between points of assessment that produces differences in the dependent variable
– Ex: Sept. 11 may affect rates of psychological disorders in children
» If we see increases in psychological disorders in a longitudinal design, are they due to age or to time of assessment differences?
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• Advantages
– Can examine stability and change in individual children’s characteristics and behavior over time
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• Disadvantages
– Non-random participant loss (selective attrition)
• Participants who finish the study differ in systematic ways from participants who drop out
– Final sample is not representative of the group
(population) researcher wanted to study—findings may not generalize
– Practice effects
• Change due to familiarity with data collection procedures rather than change due to development
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– Time-consuming and expensive
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• Cross-sectional Designs
– Multiple cohorts (and multiple ages) are examined at a single time of assessment
– Cohort and age are confounded
• Differences across cohorts may produce changes in the dependent variable
– Ex: Cohorts born in 1970 and 1990 are likely to differ with respect to early child care experiences
» If we see differences in social competence in a cross-sectional design, are they due to age or to cohort differences?
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• Advantages
– More efficient than a longitudinal design (faster, less expensive)
– No participant loss
– No practice effects
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• Disadvantages
– Cannot examine stability or change in individual children’s characteristics or behavior over time
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Complex Developmental Designs
(Sequential Designs)
• Involve complete crossing of 2 of 3 variables (cohort, age, time of assessment)
• Interpretation of data from these designs is still ambiguous– Results cannot be clearly attributed to one of the
three variables (confounding is still present)
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• Baltes (1968) argued for the use of the cohort-sequential design in studies of development
• Allows for the separation of cohort and age effects – But time of assessment is still confounded
with both factors• Baltes argues that time of assessment is unlikely
to affect data in developmental studies
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• Cohort-sequential design
– Different cohorts compared at the same ages (but at different times of assessment)
Cohort Time of Assessment
1975 1980 1985
1960 15 20
1965 15 20
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• Allows comparison of children of the same age from different cohorts
– Ex: Two groups of 15-year-olds (different cohorts); two groups of 20-year-olds (different cohorts)
• If the same-age groups are different from one another with respect to the dependent variable(s), have evidence for cohort effects
• If not, can attribute any differences to age rather than to cohort
• But both are confounded with time of assessment
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Data Collection Techniques
• Systematic Observation (2 Types)
– Naturalistic Observation
• Observe child’s behavior in a natural environment
–Exs: playground, school, home
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– Structured Observation:
• Design a situation that will elicit relevant behavior(s)
• Typically conducted in a laboratory setting (but not always)
• Observe different children in the same situation
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Coding Observational Data
– Event sampling: Every occurrence of a behavior(s) during a specified observation period is recorded
– Time sampling: The observation period is divided into intervals and the occurrence of a behavior(s) is recorded if it occurs during an interval; the same behavior is not coded twice in the same interval
• Likely to under- or over-estimate the frequency of behaviors depending on the base rate of the behavior and the size of the interval
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– Ratings: Likert-type scales are used to rate behavior(s) during a specified observation period
• Often used for “molar” behaviors (e.g., maternal sensitivity)
• Typically require a higher level of inference on the part of observers
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General Disadvantages (Observation):
• Observer Bias
– Observer records/judges behavior inaccurately in order to make it consistent with hypotheses or with other beliefs (unintentional!)
• Participant Reactivity
– Observer’s presence affects behavior of those being observed
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• Self-report Measures
– Clinical Interviews
• More “open-ended” questions—response choices are not limited
• Participants may be asked different questions (depending on their answers)
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– Structured interviews and questionnaires
• More “close-ended” questions—response choices are limited
–Ex: yes/no questions, rating scales, multiple choice questions
• All participants are asked the same questions
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• Parents, child care providers, and teachers often provide information about infants and younger children
– Ex: infant/child temperament; behavior problems; social skills
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• General Disadvantage (self-report or report by others):
– Data may be inaccurate due to• Deliberate (or semi-deliberate) deception• Misinterpretations of questions • Lower verbal skills• Memory limitations• Lower observational skills• Less knowledge about relevant behaviors
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Psychophysiological Methods
• Record physiological responses – Exs: heart rate, hormone levels (cortisol),
brain wave activity
• Infer psychological “states” from these responses (e.g., perceptions, emotions)
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Advantage:
• Can be used with preverbal infants and young children (limited language)
Disadvantage:
• Changes in physiological responses can be caused by many “irrelevant” factors (e.g., hunger, boredom, movement)