Final answer:
An observational study is a nonexperimental scientific investigation that measures characteristics in a sample without attempting to manipulate variables of interest. It is similar to epidemiological studies that do not prove cause and effect. Observational studies are cheaper, easier, and can study more subjects compared to experimental studies.
Step-by-step explanation:
An observational study is a type of nonexperimental scientific investigation where the researcher measures characteristics in a sample but does not manipulate or control variables of interest. It is similar to epidemiological studies that observe the relationship between variables without establishing cause and effect. Observational studies are often used when experiments are impossible, impractical, or unethical to conduct. They are cheaper and easier to conduct, and can study more subjects and obtain a larger set of data compared to experimental studies.