Statistics and Record World data
Although the disco chart began reporting popular songs in New York City nightclubs, Billboard soon expanded coverage to feature multiple charts each week which highlighted playlists in various cities such as San Francisco, Boston, Los Angeles, Miami, Phoenix, Detroit and Houston (among others). During this time, Billboard rival publication Record World was the first to compile a dance chart which incorporated club play on a national level. Noted Billboard statistician Joel Whitburn has since "adopted" Record Worlds chart data from the weeks between March 29, 1975 and August 21, 1976 into Billboards club play history. For the sake of continuity, Record Worlds national chart is incorporated into both Whitburn's Dance/Disco publication (via his Record Research company) as well as the 1975 and 1976 number-ones lists.
With the issue dated August 28, 1976, Billboard premiered its own national chart (National Disco Action Top 30) and their data is used from this date forward.