"….This empirical analysis shows that altered tallies were more prevalent in polling stations where the opposition was not present and in states controlled by governors with grassroots experience of managing the electoral operation."

https://www.cambridge.org/core/journals/american-political-science-review/article/fingerprints-of-fraud-evidence-from-mexicos-1988-presidential-election/8F3C1BCA4C53FE85EA48E51321E339E9/core-reader

https://archive.is/YHwtq