The Hot 100 served for many years as the data source for the weekly radio countdown show "American Top 40". This relationship ended on November 30, 1991, as "American Top 40" started using the airplay-only side of the Hot 100 (then called Top 40 Radio Monitor). The ongoing splintering of Top 40 radio in the early 1990s led stations to lean into specific formats, meaning that practically no station would play the wide array of genres that typically composed each weekly Hot 100 chart.