Study suggests most men are too small for most women (Part 1)
A 2015 study investigated women's preferences in penis size using 3D-printed cylinder models. The results showed women overestimated the average penis size and preferred penises even larger than that.
Researchers from the University of California conducted a unique study on women’s preferences in penis size in 2015 using 3D-printed cylinder models.1 The most striking results of the study were largely overlooked by the authors: the women who participated significantly overestimated the average penis size in the male population, and preferred penises larger than even their own overestimation of the average. In this review, I critically examine this study and highlight these overlooked results. In this first part, I delve into the methods, including the study design and the recruited participants.
📋 Methods
📏 Study design
If you’re conducting a study investigating women’s preferences in penis size, your first choice of method might be the traditional survey. Write a few questions about penis size and serve up the questionnaire to a group of women recruited for the purpose of answering it. The problem with such an approach, however, is the human error in correctly estimating the size of things. When this error concerns women’s estimation of penis size, the phenomenon has a name: “girl inches”.
When women try to guess or recall a sexual partner’s penis size, they generally tend to overestimate it. What a woman might guess to be six inches might turn out to be only five. Put differently, “girl inches” are a slightly smaller unit of measurement than the standard inch. When you ask women about their ideal penis size, the answers are worthless because they’re measured in the mysterious unit of “girl inches”, which also varies from subject to subject.
An improvement on traditional surveys is visual data: have women look at pictures of erect penises of various sizes and let them select one based on their preferences. Whether it be real penis images or simulated graphics, at least the subjects have a 2D representation of the object in this type of study design. But the authors of the paper we’re reviewing made an additional improvement by adding a dimension to the visuals, using 3D-printed models that could be touched and manipulated by women. This methodology was novel for the research question.
The 3D models weren’t realistic replicas of penises but simple cylinders with a dome on top to distinguish the base from the tip, printed in blue to avoid any association with skin color. The authors claimed that “making the penis model more realistic might have provoked negative responses”, but a more plausible reason for the choice might be that it’s just a lot easier to print a cylinder in 3D than a realistic penis model.
Thirty-three cylinders were printed, in sizes that varied in both length and girth. In such a study, this variation must reflect to a certain extent the actual distribution of penis size in the male population. The authors’ strategy was to start from the simplest statistic of that distribution—the mean penis size in terms of length and girth—and vary these two dimensions in both directions to get cylinders bigger and smaller in length and girth. But to do so, the authors had to choose numbers for the average penis.
Surprisingly, no one really knows what the average erect penis size is. Self-reported measurements are highly unreliable, as men tend to exaggerate their actual penis size—something the study’s authors duly noted in their literature review. Measurements by investigators in clinical settings are more reliable, but these data are scarce in the academic literature. The best estimate for erect length based on these data, measured from the pubic bone to the tip of the glans, is between 5 and 5.5 inches, and probably on the lower end of that range.2
But even with these well-known facts, the authors made a curious choice that flies in the face of their own cited references: “The average American erect penis length was estimated as 6 inches,” they wrote. In response to a reader’s criticism of this odd choice on the journal’s website, the study’s lead author, Nicole Prause, commented: “These figures are fairly close to average erect sizes in the USA so far as we know them.” That is a bizarre statement, given what we indeed know from the scientific literature.
In any case, many models were printed based on the chosen starting size of 6 inches in length and 5 inches in girth. Length and girth were varied in 10 increments of half an inch in both directions, yielding a dataset of 100 possible models in combined length and girth. But to present participants with 100 cylinders is to overwhelm them with choices. To solve this problem, only a third of the space of measurements was sampled, randomly selecting 33 models out of the 100 possibilities so that participants could make thoughtful decisions.
👥 Participants
To avoid volunteer bias, the project was advertised merely as “a study concerning sexuality” with no mention of penis size. Only 75 women participated in the study, and not all of them completed all the tasks. They were white, Asian, Hispanic, and Black, in different proportions, with a mean age of 24. It should be kept in mind that this is a small sample size, so no conclusions can truly be drawn from the results. Nonetheless, it’s amusing to ponder what the findings suggest.
The 75 women who were recruited for the study identified themselves with various sexual orientations. Only 36 identified as heterosexual, 10 identified as bisexual, 8 as lesbian, 6 as asexual, 3 as queer, and 11 “did not identify”. That sums up to 74, which leaves one woman’s datum missing for unknown reasons.
One would think that in such a study, the authors would make sure to include only the women who were sexually attracted to men. In this case, the most restrictive option would have been to include only those who identified as “heterosexual” or “bisexual”, and the most permissive would have been to count all except those who identified as “lesbian”. Surprisingly, however, no women were excluded from the data analysis.
The justification that the authors gave for this odd choice seems implausible: “Recall that participants were required to report attraction to men to participate, thus a ‘Homosexual/Lesbian’ self-identity did not preclude attraction to men.” An alternative explanation is that the $20 compensation that was promised for the volunteers’ time could have incentivized some women to participate even if they weren’t sexually attracted to men—such as those who identified as lesbian, perhaps.
In any case, the participants had, on average, 3.2 intercourse partners in the previous year, and 6 partners in their lifetime. It seems like most of the participants were young university students who had most of their sexual experiences in the year prior to the study. The women “touched” on average 6.8 penises in their lifetime, which is higher than their average number of intercourse partners, indicating that the women had some sexual partners they didn’t have intercourse with.
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➡️ Next part
In the next part, I delve into the women’s estimation of the average penis size.
Prause, Nicole, et al. (2015). Women’s Preferences for Penis Size: A New Research Method Using Selection among 3D Models. PLOS One, 10(9), e0133079.
King, Bruce M. (2020). Average-Size Erect Penis: Fiction, Fact, and the Need for Counseling. Journal of Sex & Marital Therapy, 47(1), 80–89.