The accuracy of election outcomes depends heavily on reliable vote tallies. This study examines the causes and consequences of variability in tally quality using data from Mexico's five national elections. Evidence reveals that over 40% of polling stations exhibit inconsistencies, yet these errors appear nonpartisan. The research links tally issues to three factors: lower educational attainment among poll workers, higher workload, and increased tally complexity. Additionally, combining a survey with nearly 80,000 poll workers and detailed administrative data shows that inaccuracies lead to recounts and decreased trust in electoral institutions. These findings carry significant policy implications for improving election administration.
