Developmental Research Methods

Longitudinal Design

• studies the same group of individuals (usually one age group) repeatedly over time (usually years).

Longitudinal Design

MathTestScores

Age at testing 20 30 40 60 80 Year of testing 1930 1940 1950 1970 1990

• Example: A group of adults, ages 19-21, were studied for 60 years to determine age changes in mathematical ability.

Types of Long-Term Studies

• Retrospective study – past history data

• Prospective study – longitudinal, no random assignment

• Randomized assignment study –longitudinal and experimental– random assignment to the study conditions – placebo-controlled, double-blind– e.g. drug trials

Limitations of the Longitudinal Research Design

• Time and cost. Study takes a long time to complete and is usually costly.

• Selective attrition. Participants remaining at the end of the study may differ in important ways from those who drop out along the way.

• Repeated measurement. Effects of repeated study and measurement are difficult to assess.

Cross-Sectional Research

• compares several groups of people who are different in age, but similar in other important ways at one point in time.

Cross-Sectional Research

Example: Five groups of adults were studied (say in 2006) to determine age differences in mathematical ability.

19-23 years old N=100

29-31 years old N=107

39-41 years old N=100

56-64 years old N=95

76-84 years old N=58

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100

20 30 40 60 80

Limitations of the Cross-Sectional Research Design

• Cohort effects: a generational group is exposed to the same societal influences– confounded with age

Sequential Research Design

• combines cross-sectional and longitudinal designs, allows checking and adjusting for cohort effects.

Example: Three different longitudinal studies were conducted ten years apart to determine age and cohort differences in mathematical ability.