John from Sunset Coast . I don't know how accurate the 50% figure is but this from the wiki entry on circumstantial evidence deals with the perception of such evidence being of less value than direct evidence :

"Indeed, the common metaphor for the strongest possible evidence in any case—the "smoking gun"—is an example of proof based on circumstantial evidence. Similarly, fingerprint evidence, videotapes, sound recordings, photographs, and many other examples of physical evidence that support the drawing of an inference, i.e., circumstantial evidence, are considered very strong possible evidence."


http://en.wikipedia.org/wiki/Circumstantial_evidence