This is a tricky question. In lines 4-7, the author says that Tucker "acted in 20 films and performed hundreds of times on stage as a dancer..actor." In the second paragraph, the author talks about his process for collecting background material for the book and says that he "also examined - as primary source material for an analysis of Tucker's acting technique -were the ten still available films in which Tucker appeared." (lines 23-26). Preponderance is generally understood more than 50% -think of the preponderance of the evidence standard in civil cases - therefore, since Tucker acted in 20 films, and the author only examined ten of them to analyze his acting technique, it is only 50%, not OVER 50% and is thus, not based on examination of a preponderance of the films.