## Bayes’ theorem and transgender lesbians

Some time ago I read a cool post on Tumblr, but I can’t find it anymore. It was about calculating P(trans|WLW), the fraction of women who love women that is transgender, from P(trans), the fraction of the general population that is transgender, P(WLW), the fraction of the population that is a woman-loving woman, and P(WLW|trans), the fraction of gynephillic trans women among trans people. Bayes’ theorem says

P(trans|WLW) = P(WLW|trans)P(trans)/P(WLW).

I remember that the resulting number was significant. As I could not find it again, here is a quick and dirty reconstruction. For every statistic, I picked the first one I found that did not seem completely unrealistic.

So Bayes’ theorem gives us P(trans|WLW) = 0.15.

### Bonus: suicide attempts

While preparing this post, I stumbled upon this report. Page 8 lists:

• P(attempted suicide) = 0.016.
• P(attempted suicice|trans) = 0.41.

Bayes now says P(trans|attempted suicide) = 0.26. Big if true.*

### Section of Doubt

Applying Bayes’ theorem like this seems to give unreasonably good mileage. That suggests that social scientists aren’t allowed to use numbers from different studies and get conclusions from them, or asymmetric misreporting makes these calculations error-prone.

The last number above is big. Makes one wonder why so little effort is spent explicitly targetting at-risk trans people.

* Added July 16th: I just met a subject expert, she said this figure sounded about right.

## Traveling while vegan

Whenever I start doing a new thing, I try to find other’s experiences with it and make sure I don’t gloss over any obvious pitfalls. But, somehow, I completely missed all the articles about traveling as a vegan. It is very unpleasant.

The past few weeks I have been visiting conferences for work. By itself, that is exhausting; waking up early, spending all day attending talks, meeting new people and otherwise talking shop. But being vegan somehow makes it even worse.

Getting food at a foreign grocery store is as unpleasant as first starting veganism like being a new vegan again – you have to look at all the lists of ingredients because you don’t know which products are vegan. But harder, as the ingredients are written in French.

Having lunch and dinner with colleagues is worse. If you’re unlucky, 9 out of 10 restaurants don’t serve any vegan dish. This makes having lunch with a group of people you don’t know non-trivial. You have to be loud and assertive enough to make sure they don’t go to a wrong restaurant and leave you behind. Doing so does not come naturally to me. And when people do agree to find another restaurant it is reluctantly.

Oh well. Worth it.