Researchers want to investigate whether people feel happier after exercising outside or exercising inside. Four hundred adults who already exercise regularly are randomly chosen to participate in the study. They are divided randomly into two groups. One group is asked to exercise inside at least five times a week, while the other group is asked to exercise outside at least five times a week. All participants are asked to rate their happiness on a scale of 1 to 10 at the end of each exercise session. At the end of the study, researchers compare the average happiness ratings of the outside exercise group to the average happiness ratings of the inside exercise group.

Question

Researchers want to investigate whether people feel happier after exercising outside or exercising inside. Four hundred adults who already exercise regularly are randomly chosen to participate in the study. They are divided randomly into two groups. One group is asked to exercise inside at least five times a week, while the other group is asked to exercise outside at least five times a week. All participants are asked to rate their happiness on a scale of 1 to 10 at the end of each exercise session. At the end of the study, researchers compare the average happiness ratings of the outside exercise group to the average happiness ratings of the inside exercise group.
Why is random assignment important in this study? In your explanation, give an example of how this experimental study could have been designed differently where assignment was not random. Why would this be a problem?

GPT-4o mini · Answer

Random assignment is crucial in this study because it helps to ensure that the two groups (those exercising outside and those exercising inside) are equivalent at the start of the experiment. This means that any differences observed in happiness ratings at the end of the study can more confidently be attributed to the type of exercise environment rather than pre-existing differences between the participants. Random assignment minimizes selection bias, helping to control for confounding variables that might influence the results.

For example, if the researchers decided to assign participants to exercise environments based on personal preference (for example, those who prefer outdoor exercise are assigned to the outside group while those who prefer indoor exercise are assigned to the inside group), this would lead to a non-random assignment. In such a design, the outside group might include participants who are naturally more inclined to enjoy exercise and might rate their happiness higher regardless of the setting. In contrast, those in the inside group might already have a tendency to be less enthusiastic about exercise and might rate their happiness lower.

This non-random assignment could create a confounding variable that skews results, making it difficult to determine whether the differences in average happiness ratings were genuinely due to the exercise environment or were simply reflective of the participants’ inherent differences in preferences or attitudes toward exercise. Thus, random assignment helps to ensure that each group is balanced in terms of such variables, allowing for a more accurate and reliable comparison of the effects of exercising indoors versus outdoors on happiness.