Answer:
Introducing a change to the subgroup
Explanation:
Given there are four statements. We have to find the one which represents one of the differences between an experiment and an observational study.
The answer is option 2. Introducing a change to the subgroup
Experimental and observational studies are both types of studies between which a number of differences can be identified. When conducting research studies, various types of research in order to arrive are adopted according to the need.
An experimental study is a study where the researcher has control over most of the variables.
On the other hand, an observation study is a study where the researcher cannot control any variable but merely observes the subject without controlling any variables.