Amount of information on case illustrations in self-help psychology books

40 books on self-help psychology were examined in a 2 x 2 multivariate analysis of covariance design for the number of case illustrations, number of lines of text about case illustrations, and average number of lines per case illustration. The covariate was pages per book and the independent variables were status of the book (bestseller or nonbestseller) and decade of publication (1970-1979 or 1980-1989). It was hypothesized that bestsellers would contain more case illustrations and lines of text describing case illustrations than nonbestsellers. Case illustrations per book in nonbestsellers increased significantly in number over the two decades when compared to bestsellers.