Final answer:
An observational study is a nonexperimental scientific investigation where characteristics are measured without manipulating variables. Comparing vaccination schedules of patients with and without autism would be an example of an observational study.
Step-by-step explanation:
An observational study is a type of nonexperimental scientific investigation in which the researcher measures characteristics in a sample without attempting to manipulate or control variables of interest. This type of study compares different groups of subjects based on their exposure or characteristics, without any attempt to influence or modify those exposures or characteristics.
In the case of comparing vaccination schedules of patients with autism to those without autism, it would be an example of an observational study. Researchers would measure and compare the vaccination schedules of both groups to see if there are any differences that may be associated with autism.