In a longitudinal design age is treated as a ______ variable, but age is treated as a ______ variable in a cross-sectional design.
A) within-subjects; within- and between-subjects
B) within- and between-subjects; between-subjects
C) within-subjects; between-subjects
D) between-subjects; within-subjects

Question

Quizplus · Accepted Answer

In a longitudinal design, the same individuals are observed or measured over time, so age is treated as a within-subjects variable because changes in age are being tracked within the same individuals. 
In contrast, in a cross-sectional design, different individuals with different ages are measured at one point in time, so age is treated as a between-subjects variable because age differences are being compared between different individuals.

In a Longitudinal Design Age Is Treated as a ______