Discuss at least two common issues that can affect the validity of experimental studies. Include an example for each.
1. Selection bias: This occurs when the participants in a study are not representative of the population to which the results will be generalized. For example, if a study on the effectiveness of a new drug only includes participants who are young and healthy, the results may not be applicable to older or sicker individuals who are more likely to use the drug in real-world situations. This can lead to inaccurate conclusions about the drug's effectiveness and safety.
2. Confounding variables: These are extraneous variables that are not accounted for in the study design but can influence the outcome of the study. For example, if a study examines the impact of exercise on weight loss but fails to control for participants' diet habits, the results may be confounded by the fact that some participants may be eating unhealthy foods that counteract the effects of exercise. This can lead to inaccurate conclusions about the relationship between exercise and weight loss.