Final answer:
Observational studies do not manipulate variables and measure characteristics in a sample, while experiments apply a treatment to a group of subjects and compare them with a control group.
Step-by-step explanation:
The main difference between observational studies and experiments is how subjects are treated. In an observational study, no attempt is made to influence the subjects in any way, while in an experiment, the researcher applies a treatment to a group of subjects and compares them with a control group. An example of an observational study is a political poll, where characteristics of a sample are measured without manipulating variables. On the other hand, an example of an experiment is giving a vaccine to one group of children and a placebo to another group, to determine its effectiveness in preventing polio.