What term describes an experiment where one or more factors are manipulated?

A controlled experiment is specifically designed to test the effect of one or more independent variables while keeping other variables constant. This manipulation allows for a clear understanding of causal relationships. For example, if a researcher is investigating the effect of sunlight on plant growth, they would manipulate the amount of sunlight received by different groups of plants while keeping other factors, such as water and soil type, constant.

This design ensures that any observed changes in the dependent variable (in this case, plant growth) are attributable directly to the manipulation of the independent variable (sunlight exposure). The term "controlled" emphasizes the importance of maintaining consistent conditions to accurately isolate the effects of the manipulated factors.

In contrast, the other choices refer to broader concepts that either don't specifically focus on the manipulation of factors or signify different aspects of experimental methodology. Therefore, the term "controlled experiment" is the most accurate descriptor for the scenario presented.