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Recent research supports Jefferson's claim. Brunetti and Weder found "evidence of a significant relationship between more press freedom and less corruption in a large cross-section of countries." They also presented "evidence which suggests that the direction of causation runs from higher press freedom to lower corruption." Adsera, Boix, and Payne found that increases in newspaper readership led to increased political accountability and lower corruption in data from roughly 100 countries and from different states in the US.

About 100 countries and what else was information gathered from to show that more people reading newspapers had higher political accountability?
different states in the US.