Verified by 
In one chapter of my forthcoming book (June 2011), The Consuming Instinct: What Juicy Burgers, Ferraris, Pornography, and Gift Giving Reveal About Human Nature, I discuss how the effects of morphological features (e.g., height, breast size, facial dominance, digit ratio) manifest themselves in the marketplace.
While conducting research for the chapter in question, I came across an interesting study that linked penis size (a morphological trait) to a specific sexual behavior. Christian Grov, Jeffrey T. Parsons, and David S. Bimbi surveyed 1,065 gay or bisexual men about their penis size and a broad range of variables (e.g., sexual health, psychosocial adjustment, and sexual preferences).
One finding that struck me as particularly interesting was the relationship between a man's perceived penis size (see here for an earlier post that I wrote on this topic) and the extent to which he was an "inserter" (top) or "insertee" (bottom), in terms of anal sex. The researchers asked the following question: "Do you consider your penis size to be...?" with possible answers being "below average," "average," "above average," and "way above average." The last two categories were fused into one "above average" category. They were also asked about their preferred sexual roles as relating to anal sex. The five possible answers were: Top 100 percent; Mostly Top; Versatile 50/50; Mostly Bottom; and Bottom 100 percent. The five original categories were fused into three categories: Top and Mostly Top became Top, Versatile remained as is, and Bottom and Mostly Bottom became Bottom. Here are the results:
Top
Below Average: 29.2 percent
Average: 30.7 percent
Above Average: 41.6 percent
Versatile
Below Average: 31.9 percent
Average: 40.5 percent
Above Average: 37.8 percent
Bottom
Below Average: 38.9 percent
Average: 28.8 percent
Above Average: 20.6 percent
The two variables were statistically linked (p < .001). "Below Average," "Average," and "Above Average" men were more likely to be Bottom, Versatile, and Top respectively.
As the authors proclaim early in the paper, penis size has long been symbolically associated with masculinity. Hence, to the extent that these different sexual positions are perceived as more "masculine" (top) or more "feminine" (bottom), it might seem reasonable to expect a link between these two variables. On a related note, in some cultural settings, being gay is largely associated with being the bottom. A similar attribution has sometimes been made within the confines of prison culture.
