Final answer:
In an appropriate designed experiment, the scientist is able to test the effect of the independent variable.
Step-by-step explanation:
In an experiment, the scientist is able to test the effect of the independent variable. The independent variable is the factor that the scientist manipulates or controls in order to study its effect on the dependent variable. The dependent variable is what the scientist measures to see how much effect the independent variable had. The control group is a group that does not receive the experimental manipulation, and the sample size refers to the number of participants or subjects in the study.