Inability to Manipulate Variables

What is a critical requirement regarding the independent variable for a study to be classified as a true experiment?

A researcher wants to study whether journaling improves mental health. She recruits 200 participants and finds that 95 of them already keep a daily journal while the remaining 105 do not. She measures each group's mental health scores and compares the results. This study qualifies as a true experiment because it compares two distinct groups on a dependent variable.

Match each research scenario with the correct methodological classification and rationale regarding the use of active manipulation.

A researcher notices that honors students listen to classical music more often and have higher grades than non-honors students. To determine if music causes better performance, the researcher must design an experiment. Arrange the steps of this design to show how active manipulation logically rules out pre-existing differences (like academic ability) as alternative explanations.

A researcher evaluating the validity of a study on 'brain-training apps' rejects the claim that the apps cause memory improvement because the study merely compared regular users to non-users. The researcher notes that for a true experiment, the design requires active _____, a step necessary to rule out pre-existing differences in motivation or cognitive ability as alternative explanations for the results.

A researcher is designing a study to test if 'mindfulness meditation' increases empathy. Currently, they observe that members of meditation clubs score higher on empathy scales than non-members. To create a true experiment that utilizes active manipulation to eliminate the alternative explanation that 'naturally empathetic' people are simply more drawn to meditation, which protocol should the researcher construct?

Merely comparing pre-existing groups of participants (such as comparing individuals who already keep a journal with those who do not) constitutes active manipulation of the independent variable in a true experiment.

Match each concept related to research methods with the statement that best explains its role in determining whether a study is a true experiment.

A psychologist notices that people who voluntarily practice mindfulness meditation report lower levels of depression than non-meditators and concludes that meditation reduces depression. A methodological critique of this study would point out that she never _____ the independent variable—the defining step that separates a true experiment from a correlational comparison—and therefore cannot eliminate the possibility that naturally less-depressed individuals are simply more inclined to choose meditation in the first place.

A peer reviewer is evaluating a published study that concludes 'journaling causes reduced anxiety.' The study compared anxiety scores of people who already kept a daily journal with those who did not. Arrange the following evaluative steps in the most logical order to judge whether the causal conclusion is warranted.