American Institute of Certified Planners (AICP) Practice Exam

What does the manipulation of an independent variable allow an experimenter to do?

1. Control at random levels

2. Analyze past data

3. Establish causal relationships

4. Define the population

The correct answer is: Establish causal relationships

The manipulation of an independent variable is a fundamental aspect of experimental design in research. By changing the independent variable, an experimenter can observe how these changes affect the dependent variable. This process is crucial for establishing causal relationships, as it allows the researcher to determine whether variations in the independent variable directly lead to changes in the dependent variable. For example, in a study examining the impact of different fertilizers on plant growth, the type of fertilizer is the independent variable. By manipulating this variable and measuring the resultant growth (the dependent variable), the experimenter can draw conclusions about the effectiveness of each fertilizer type. The context of the other options highlights the specific focus of this question on establishing causality. Controlling at random levels pertains more to sampling methods or ensuring experimental rigor but does not directly link to the effects deemed causal. Analyzing past data typically involves observational studies rather than manipulative experiments. Defining the population relates to the characteristics of the sample being studied rather than the causal relationships equipped through manipulation of variables.