Why is the threat of subject attrition more problematic in longitudinal designs than in other types of descriptive research?
a. Subjects are elderly.
b. Data analysis is complex, and missing data points necessitate dropping the subject from the analysis.
c. Data collection occurs over a much longer period of time.
d. There is selection bias because of the study requirements.
ANS: C
Longitudinal designs examine changes in the same subjects over time. They are expensive and require a long period of researcher and subject commitment. Measurement must be carefully planned and implemented, because the measures will be used repeatedly over time. There is often a bias in selection of subjects because of the requirement for a long-term commitment. In addition, loss of subjects (attrition—subject quits participating in the study) can be high and can decrease the validity of findings.
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