The Beatles Believability Index (BBI) is a rating system for the analysis of solo-Beatle songs and fantasy Beatles album projects. Its purpose is to rate how convincing a particular song or album compilation is when being presented as a Beatles product. It can be applied to individual songs, fantasy compilations or complete fantasy discographies.

Individual songs receive points for style precedence (does it sound like something they have done or might have done?), lyric content and the number of former Beatles actually present. For instance, "Working Class Hero" loses points for the swear words whereas "I'm The Greatest" gains points for having 3 out of four Beatles present (John, George and Ringo) as well as two fringe Beatles alumni (Billy Preston and Klaus Voorman).

Fantasy albums are critiqued on the accumulated BBI of the individual songs, the time frame covered by the individual songs (release date, recording date or the composing dated), overall feel and flow of the album and any included back story. These same criteria can then be extended to complete discographies.

BBI (Beatles Believability Index)
0 - There's no way
1 - I have my doubts
2 - I think I hear...
3 - It could go either way
4 - Isn't that...?
5 - I swear it's them