In a cohort study designed to explore the relationship between academic achievement and heavy alcohol consumption among college students, every attempt was made to follow 1,000 students during their collegiate careers. Participants were asked to periodically report alcohol consumption and alcohol-related behaviors. After 4 years, significant findings demonstrated a causal relationship between poor academic performance and heavy alcohol consumption. However, findings were only reported for 426 participants due to a high dropout rate for the study. What is most likely the source of error in this study?
The placebo effect
Reporting bias
Selection bias
Random variation