who’s doing the measuring
Next, you have to ask; who’s doing the measuring? A white-coated scientist, a bikini-clad babe, or the subject himself? Perhaps the most famous and oft quoted study was conducted by Alfred Kinsey in the 50s and 60s. Kinsey provided 3,500 subjects with postcards against which they were to mark the maximum extent of their erection. About 2,500 men responded and the average turned out to be 6.25 inches in length. Another study using similar methodology in 1996 got similar results (6.38 inches).
The problem here is what has become known as “self-reportage bias.” Even when assured that the results are completely anonymous, guys tend to exaggerate. You’d think it would be the opposite. That they’d deliberately underestimate the size of their penises in order to skew down the average size to which they would then compare themselves more favorably. Self-reportage bias is a real phenomenon and has been observed in numerous surveys on everything from drinking habits to stated income. In fact, a whole school of statistical analysis has developed on how to adjust for this bias.