Umbrellas cause ejaculation

Sex with 21 Women Lowers Risk of Prostate Cancer


I saw this story reported today and it stuck me as particularly poor science. As click bait, it is irresistible. It has it all: sex, cancer, an excuse to use the word ejaculation and the conclusion that promiscuity is better than monogamy, unless you're gay.

The study found that men who had slept with more than 20 women had significantly lower instances of prostate cancer than those men who slept with less.

I have no reason to doubt the numbers.  But many reports of the findings illustrate the classic fallacy of confusing correlation with causation.  I have noticed that on on days when lots of people carry umbrellas, the buses are much fuller.  But it would be wrong to jump to the conclusion that umbrellas cause busses to fill up, and that increasing the  number of umbrellas on our streets would improve bus company revenues.  It is similarly incorrect to conclude that the full busses cause people to carry umbrellas. There is only correlation, no causation. It could be that there is some third factor that is the cause of both: like rain.

Similarly it is unreasonable to conclude that more sexual partners means less cancer.  There is only correlation, not causation.

I'm curious about how the count was calculated. Did they ask men how many women they had sex with up to a particular time, and then follow them to see which developed cancer? Did conquests after that date count towards the total?  It would not come as a huge shock to me to learn that men with cancer don't sleep around as much and those who don't have cancer, what with the illness, surgery, treatment and all.

Even if the numbers are good there may be unknown variables influencing both the number of partners and and the incidence of prostate cancer.  A headline that said "study discovers that drinkers have more sex" would scarcely raise an eyebrow. What if drinking alcohol, somehow, reduced the chances of getting this cancer?  Suppose weight was a contributing factor.  Maybe fat guys don't have as many sexual partners as slim ones.  It's possible. Maybe happy men have more partners, and happy men get cancer less.  That's possible too. Maybe guys with large penises sleep with more woman, and penis size is a factor in prostate cancer. Maybe condoms are a contributing factor. Men in monogamous relationships are less likely to wear condoms during sex, than guys on one night stands.

One explanation offered by Dr. Marie-Elise Parent was that "having many female sexual partners results in a higher frequency of ejaculations".  This is quite bizarre.  It might make some sense if each partner were available for only one ejaculation. The majority (but not all) of the women I have had sex with were up for quite a few more than the one ejaculation.  And I suspect that I am not unusual in that regard. Furthermore I have it on good authority that most men are able to ejaculate in the absence of a partner. And considering the periods in my life when I had a partner and when I didn't, I might go so far as to say that maybe having a partner results in reduced frequency of ejaculations.

But don't jump to any conclusions. And beware of umbrellas. 


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