Final answer:
An observational study is a nonexperimental research design where the researcher measures characteristics in a sample without manipulating variables of interest. It does not involve random assignment of participants to groups.
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. In contrast to an experiment, there is no random assignment of participants to groups in an observational study. This type of research design is often used when randomization is not feasible or ethical.