Answer:
The answer is longitudinal research.
Explanation:
Longitudinal research is done over a period of time and usually involves observing a small group of subjects. These are especially common in social sciences such as sociology and psychology, although other areas like medicine also use longitudinal studies to examine the effects of diseases or treatments.
The greatest advantage of longitudinal studies is that they are often unexpensive and highly reliable, as they involve constant and rigurous observation. However, they are naturally time consuming and might not accurately reflect larger populations.
