What factor can potentially threaten the validity of a study?

High attrition rates can significantly threaten the validity of a study because they indicate that a substantial number of participants are dropping out or not completing the study. When individuals leave a study, it can lead to a biased sample, as the remaining participants may have different characteristics or outcomes than those who withdrew. This loss of participants can skew the results and affect the generalizability of the findings. It raises concerns about whether the study's outcomes are representative of the broader population, ultimately undermining the strength of the conclusions drawn.

In contrast, high compliance rates and low attrition rates support the reliability of a study by ensuring that most participants complete the necessary steps, leading to more robust data. Randomized control trials, when conducted properly, are designed to minimize biases, including those related to participant dropout. Thus, the presence of high attrition rates is a clear indicator of potential validity issues within a study.