Explain how psychologists can use both longitudinal studies and cross-sectional studies to examine human behavior across the life span. Give an example of each.

Psychologists use longitudinal studies when they restudy the same group of people over a long period of time. For example, psychologists use longitudinal studies to understand how a group of people who are all associated in a way will develop over time. Cross-sectional studies are useful because they compare people of different ages. This is could be seen in mental health experiments, behavioral differences between ages, and physical health charts. 

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