Final answer:
The independent variable is the factor that a scientist varies for different groups in an experiment to observe its effects on the dependent variable. This systematic variation is the only difference between the experimental and control groups, allowing the isolated study of this variable's impact on the experiment's outcome.
Step-by-step explanation:
The independent variable in an experimental study is defined as the factor that is manipulated or controlled by the scientist conducting the experiment. To ensure the validity of experimental outcomes, the independent variable is the only element that is systematically varied to examine its effect on the dependent variable. In the context of the student’s question, the correct answer is: A) varies for different groups in an experiment.
The independent variable is what the researcher changes deliberately to probe the effects of such manipulations. For example, when studying the impact of fertilizer on plant growth, the type of fertilizer used would be the independent variable. The growth of the plants, which is measured in response to these changes, is the dependent variable.
In experimental design, it's crucial to keep other potential influencing factors (control variables) constant across all groups to isolate the effects of the independent variable. When statistical analysis reveals significant differences between the groups, a scientist may conclude that the independent variable has had an effect on the dependent variable.