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 selection important in this study? In your explanation, give an example of how this experimental study could have been designed differently so that selection was not random. Why would this be a problem?

GPT-4o mini · Answer

Random selection is important in this study because it helps to ensure that the participants in both groups are representative of the population of interest. By randomly choosing participants and assigning them to either the outside exercise group or the inside exercise group, researchers can control for confounding variables that might otherwise affect their outcomes. This means that any differences in happiness ratings between the two groups can be more reliably attributed to the type of exercise they are doing (inside vs. outside) rather than other factors like age, fitness level, or baseline happiness.

If the study had been designed differently, such as by selecting participants based on their preference for exercising indoors or outdoors (for example, only including people who already preferred one type of exercise), this would introduce a selection bias. In this case, individuals who prefer exercising outdoors might already have higher baseline happiness levels than those who prefer indoor exercise. Consequently, their happiness ratings after exercising outside may be inflated, making it appear that outdoor exercise is more beneficial for happiness than it truly is. This would impair the internal validity of the study, leading to incorrect conclusions being drawn about the relationship between exercise environment and happiness.

In summary, random selection is crucial for minimizing bias and ensuring that any observed differences in outcomes are due to the intervention (type of exercise) rather than pre-existing differences in the participants themselves.