Final answer:
An observational study is a nonexperimental investigation that measures characteristics in a sample without manipulating variables. It is commonly used when experiments are impractical or unethical. They provide valuable information on naturally occurring phenomena.
Step-by-step explanation:
An observational study is a type of nonexperimental scientific investigation in which the researcher measures characteristics in a sample without manipulating or controlling variables of interest.
For example, if researchers want to investigate whether taking aspirin regularly reduces the risk of a heart attack, they may recruit 400 men between the ages of 50 and 84. The men are randomly divided into two groups: one group takes aspirin, and the other group takes a placebo. The researchers then observe and compare the number of heart attacks in each group.
Observational studies are often used when conducting experiments would be unethical, impractical, or impossible. They provide valuable information on naturally occurring phenomena and can involve large sample sizes and more subjects than experimental studies.