To examine whether depression is stable or changes with age, Dr. Bleu followed one group of participants from age 8 to age 40. This is an example of a design.

The answer is longitudinal design.

Explanation:

Longitudinal designs are a type of research which is involves observation of the same subjects over a period of time. These studies are useful tools for social sciences such as sociology and psychology, although they are often used in exact sciences like medicine to examine the effects of treatmens or diseases.

The greatest advantage of longitudinal studies is their high validity, as they involve rigorous observation of the same individuals; however, they are naturally time-consuming and might not reflect the characteristics of larger populations.

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