Which of the following best defines an independent or manipulated variable?

An independent or manipulated variable is defined as a variable that is purposefully changed by the experimenter to observe its effect on another variable, typically the dependent variable. This intentional alteration allows researchers to establish cause-and-effect relationships within their experiments.

For instance, if a scientist is testing the effect of different amounts of sunlight on plant growth, the amount of sunlight would be the independent variable because it is the factor that is varied to assess its impact on the growth of the plants. By changing this variable, the researcher can collect data to determine how it influences the outcome of interest, which in this case is the plants' growth.

Understanding this concept is crucial for designing experiments effectively and critically analyzing the results, as it allows practitioners and students in fields such as veterinary science to assess various factors affecting animal health, behavior, and physiology through controlled studies.