As pretty much everybody knows, in the wake of the allegations against Harvey Weinstein, women have been posting #metoo stories on social media sites - claims that they've been sexually harassed or assaulted in the past. A common reaction to this is to say, 'Gosh, I didn't realise how bad the problem was! Women are being assaulted all over the place!' It's an understandable reaction, but it's based on a basic error of social science methodology.
In polling, the gold standard for junk science is a self-selecting poll, where instead of asking a random sample of people what their experiences of something have been, you get people to volunteer for your study. The reason this kind of poll is so worthless is because the people who are already concerned about something are more likely to call in. So if I invited everyone who's ever had a run-in with a cyclist to tell me about it, and didn't ask anyone else about their experiences, I'd probably end up with a survey in which the vast majority of the people surveyed had had run-ins with cyclists.
Now, that pretty clearly wouldn't necessarily mean that we have a big problem with cyclists in our society. We might have a problem with cyclists; but my poll wouldn't be evidence for that, because I didn't take any care to make sure it was properly representative. All my poll would show is that there's a certain number of people out there who are upset enough about cyclists to volunteer for my survey.
Ditto for sexual assault and harassment. Doubtless there are some men who assault and harass women, but some women posting stories on social media isn't a good way of figuring out how many of them there are.
There's also, of course, the problem that #metoo stories have including everything from actual rape (physically coerced sexual intercourse) to remarks that a woman found 'uncomfortable' (or later decided to interpret as 'inappropriate'). The problem with definitions makes the movement even more useless as a barometer of the real level of sexual assault and harassment. What number of these claims actually reflect things that most people would take seriously? We don't know.
Finally, of course, we don't know what percentage of these stories are true. Again, doubtless some of them are true; but there's no way of knowing, just from social media, what proportion. Some sexual assault and harassment does occur, but we knew that already, and #metoo in itself shouldn't lead people to believe that these things are happening at a much higher rate than we thought.
Sam Butler is an English settler in New Zealand, a writer and an anti-intellectual.