Obviously, in any scientific study, it’s not just the data that’s collected, but also the means by which it is collected. If one were going to conduct such a study involving 300 men, it matters how the measurements are performed, and we all know it. Do you have the subjects of study measure their penises themselves or do you have a medical practitioner measure them? Both means of data collection are tainted right off the bat. In the even of them measuring their penises themselves, one would have to have a considerable margin of error to account for the potential exageration of the test subjects. Then, if you have a medical practitioner do the measuring, men with relatively small penises may not volunteer for the study as a result of embarassment, thus tainting the experiment. Furthermore, men who are well endowed, because of the sense of self esteem they posses, would rush into line for the study(as someone else here had mentioned).
So, how does one solve the problem? Take the measurements without their knowledge? What are you going to do, administer cialis to 300 comatose men in hospitals and conduct the study that way? As a result of these problems, I seriously doubt any of us will ever know for sure what the true average is.