Observing many students using difference-in-differences designs on the same data and hypothesis reveals a hidden universe of uncertainty

The recent advent of many-analysts studies highlighted significant variation in research outcomes when multiple teams independently explore identical datasets and hypotheses. This paper contributes to this emerging research paradigm by demonstrating how the many-analysts framework can be incorporated into social science methods classes and by pioneering its use in difference-in-differences (DiD) designs. By engaging students in independent DiD analyses on a specific research question, in this case related to local governance, the study uncovers a broad range of effect sizes and diverging conclusions reported by the analysts, highlighting the subjective nature of analytical choices and their potential impact on research outcomes. This variability underscores the importance of critical thinking and methodological rigor in social science education. The implications extend beyond pedagogy, suggesting that causal inference methods with significant researcher discretion such as DiD designs benefit from robustness analysis with multiple independent analysts.