Define, and identify the strengths and weaknesses of a cross-sectional and longitudinal

design.

What will be an ideal response?

In the cross-sectional design, the researcher assesses different-aged people at the
same time of measurement. This design is very economical, and allows researchers
to gather developmental data quickly. Unfortunately, one can only posit age
differences, because of potential cohort differences between the age groups. In this
design, age is confounded with history or cohort. In the longitudinal design, the
researcher studies one age group over time. This type of study is more costly and
time consuming than the cross-sectional study, and the researcher must be concerned
with selective dropout, testing, and possible societal changes that may affect the study
results (AKA time of measurement effect). However, the researcher, with proper
controls, can make a stronger case for the documentation of normative age-graded
influences than the researcher that uses a cross-sectional design.