The penis size study we’ve been waiting for? Analyzing a new study 15,521 penises strong
[dropcap]O[/dropcap]ne of the more exciting and publicized studies on penis size in recent memory was published in 2015 and titled: “Am I normal? A systematic review and construction of nomograms for flaccid and erect penis length and circumference in up to 15,521 men.” I’ll admit it, I was fired up when I read the title. I’ve written previously about the dearth of reliable data on the penis–especially the erect penis. My immediate reaction when I came across this study was: “finally, we can settle the erect penis size debate once and for all!” At least, that’s what I thought.
The researchers didn’t have to get their hands dirty i.e. they didn’t have to measure any penises themselves. This is a study that brings together previously published penis size studies in an attempt to garner deeper understanding and insight. The researchers looked at all previously published studies on flaccid and erect penis dimensions and put them through a set of criteria for potential inclusion in their analysis. The criteria for inclusion was quite thorough. To ensure I do it justice, below is exactly how it’s described in the study.
Criteria for study inclusion:
1. Quantitative measurement of penis size was measured by a health professional.
2. The sample included a ≥50 participants.
3. Participants were aged ≥17 years.
4. A mean and SD of the sample size measurements were provided.
5. Flaccid or erect length was measured from the root (pubo-penile junction) of the penis to the tip of the glans (meatus) on the dorsal surface, where the pre-pubic fat pad was pushed to the bone.
6. Flaccid stretched length was measured as above while maximally extending the penis.
7. Flaccid or erect circumference (or ‘girth’) was measured at the base or mid-shaft of the penis, (and not from the corona).
8. They were published in the English language.
Studies were excluded if there was any possible bias in penis size measurements caused by the study samples or the measurement procedure, such as if participants within the study sample had:
a. Any congenital or acquired penile abnormality (e.g. Peyronie’s disease, hypospadias, intersex, hypospadias, phimosis, penile cancer, previous penile or prostatic surgery).
b. A complaint of small penis size or seeking augmentation.
c. Erectile dysfunction.
d. A self-measurement reading rather than a measurement taken by a health professional.
e. Measurements made from cadavers.
Like i said, it’s quite a thorough set of criteria! I agree with basically all of it, with the exception of number 5 (more on that shortly). I was happy to see that the researchers omitted studies where the men measured themselves. As I detailed in a previous post, men trying to measure their own penises either screw up the measurement process or they just plain exaggerate.
The authors outlined which studies made the cut for each penile dimension, but to my surprise only 4 studies were used for erect penis size! I was disappointed to read that the total sample size used for erect length sums to only 432 men.
What happened to the 15,521 penises I was promised? It turns out, the 15,521 number actually refers to the total sample size of the studies used for any of the penile dimensions, including flaccid and stretched length. Most of the data refers to flaccid and stretched length, which is not a surprise since it’s much easier to measure the penis in those states.
Remember I mentioned that I didn’t agree with criteria #5? Here’s how it’s described in the study:
Flaccid or erect length was measured from the root (pubo-penile junction) of the penis to the tip of the glans (meatus) on the dorsal surface, where the pre-pubic fat pad was pushed to the bone.
It’s the last part of that sentence that messes everything up. As I’ll discuss in a future post on the influence of body fat on penis size, men have a 2 to 5 cm pad of fat located behind their penis. If a man gains weight, his fat pad increases in size and literally pulls his penis into his body (like it’s eating his penis…sorry for the visual), making it look smaller. As if guys didn’t already have enough motivation to stay in shape! To analyze penis length that’s not influenced by current body fat levels, some studies will measure the penis by pressing down on the fat pad and starting from the pubic bone (which is sometimes called the functional penis length).
Personally, I don’t agree with that approach–it’s fine to measure a man’s penis length that way (it usually makes a guy feel better to hear that their true penis length is larger than what they thought…that there’s a big penis hidden inside all of us!), but bone-pressed shouldn’t be the primary measure. I mean, I have a beautiful set of abs, but they just happen to be buried under some stomach fat; do I still get credit for having a six pack? The portion of a man’s penis buried under his fat pad can’t be seen by him or his partners and is basically unusable; so there’s no point in giving him credit for it in a study like this.
Getting back to the Veale et al. study, because of their chosen bone-pressed measurement method, their results will be higher than studies using the more common measure of penis length that measures from the base of the penis (otherwise known as the pubo-penile skin junction). I’ve drawn a beautiful diagram in MS Paint below. The bone-pressed method used in Veale et al. pushes the area in yellow all the way to the pubic bone.
A summary of the 4 studies used for erect penis length is below:
Weighted by the number of men in each study, the mean erect penis length was 13.12 cm or 5.2 inches–significantly less than the 6 inches (15.2 cm) commonly quoted as the average erect penis length. The shortest erect penis in the 4 studies measured 7.5 cm (3 inches) and the longest measured 19.0 cm (7.5 inches).
OK, time to address the elephant in the room…more like the elephant penis in the chart! Yes, I’m talking about the much larger mean erect penis length reported by the German study. Are German men packing larger Fleischgewehr‘s than the rest of us? I investigated whether something else could be responsible for the significant difference in length.
Below is a graphical summary of the mean erect penis lengths of the 4 studies used in Veale et al.
After reading through the 4 studies, I was able to solve the mystery of the giant German Würstel. It turns out German men don’t have larger schwanz‘s than the men in these other countries (at least according to the 2001 Schneider et al. study); the German study used a more generous measurement technique. Despite the criteria in Veale et al. stating that they only included studies that measured from the pubic bone, the German study is the only one that actually did. The mean erect penis length values from the other 3 studies were measured from the base of the penis–the fat pad depth is not included–which explains their shorter average lengths.
The 1996 study from Wessells et al. separately measured the fat pad depths of its male subjects. To help level the playing field with the Germans, I’ve added the mean fat pad depth to the mean erect penis length calculated from the base of the penis in the Wessells et al. study.
After adding the mean fat pad depth, the mean functional erect penis length of the American study is 15.8 cm, which is 1.3 cm larger than the mean functional erect penis length of the German study. Mystery solved!
The inconsistency in measurement methodology is unfortunate and muddies the results of an otherwise good and well-intentioned study. The mean erect penis length calculated in the Veale et al. study of 13.1 cm (5.2″) is slightly larger than the 12.8 cm (5.0″) that’s calculated if the Schneider et al. study is removed.
The researchers took the weighted mean and pooled standard deviation (13.1 cm and 1.7 cm) and simulated a normal distribution using 20,000 data points. I would do the same thing to create a proper distribution for analysis using summary statistics if the underlying data was normally distributed. The researchers used their data distribution to create a nomogram, which is the most effective way to display a variable’s distribution by percentile (I usually refer to nomograms by another name, cumulative probability distribution functions/curves on Statgasm!). An example of a nomogram looks like this:
All in all, this is a relatively simple but much needed study that brought together existing publications on penis size. The same study also analyzed flaccid length, stretched length and erect circumference; all of which I will address in future posts. The 13.1 cm (5.2″) mean erect length derived is slightly higher than it should be because of measurement inconsistency but the impact of the oversight is minor. Nonetheless, the 13.1 cm mean erect penis length number will be a pleasant surprise to a lot of guys and it’s significantly less than the 6 inches commonly quoted in popular media and what’s been reported in self-measurement studies. If you’d like to review the nomograms produced by the Veale et al. study, read the full journal article for free here.
Veale, D., Miles, S., Bramley, S., Muir, G. and Hodsoll, J. (2015), Am I normal? A systematic review and construction of nomograms for flaccid and erect penis length and circumference in up to 15 521 men. BJU Int, 115: 978–986. doi:10.1111/bju.13010
Penile length in the flaccid and erect states: guidelines for penile augmentation. J Urol1996; 156: 995–997, , .
Does penile size in younger men cause problems in condom use? A prospective measurement of penile dimensions in 111 young and 32 older men. Urology 2001; 57:314–318, , , , .