Have a look at this interview:
3 Tips for Decoding Condom Size | Condom Monologues
"CM: In your investigation into penis size, you explain that very few studies sponsored by condom companies actually produce sound scientific data. In fact, average penis size may be smaller and more varied than companies have previously reported. Please cite which penis size survey(s) you trust the most and why?
CSF: First I would like to be perfectly clear: penis size is not interesting “per se”, especially length, which is what most people mean when talking about size. You have 3 kinds of studies:
1) self-reported measurements: men report their penile dimensions. The averages are typically 15.6–16.6 cm for length and 12.2–13.6 cm for girth.
Examples: Kinsey study, Internet survey by Richard Edwards, Durex survey.
These studies are of poor interest and rather have readers feel inadequate due to the somewhat high over-estimates.
2) pharmacological measurements: measurements are conducted by researchers , either directly or by men after a proper training. The averages are typically 12.9–14.5 cm for length and 11.9–12.3 cm for girth.
They are of great value, but one needs to get the whole article to judge the quality: some have been performed on men with erectile dysfunctions, some use a very small sample, where representation is heavily questioned, methods of measurements often vary (base, mid-points, under the glans, “bone pressed” or not), or the measurement itself is different (width, circumference, and mode of erection).
The Wessells and the Schneider studies are very good examples.
3) The last kind is a hybrid between a) and b). These are the self-reported studies where:
the sample has been carefully selected (or big enough to cancel the possible bias), a harmonized measurement method is clearly explained to ensure standard practices and avoid inconsistencies, men are motivated to measure their penis carefully and to report accurate data. The averages are typically 13–14.2cm for length and 12–12.2 cm for girth. The Herbernick and TheyFit studies are good examples. Their values reside in the huge samples from which they get the data.
There is no survey I trust the most. Rather, it is the consistency through the various serious surveys which should be trusted."
