Prepare to un-learn what you might have been told in Year Six PSHE: the myth that close female friends menstruate in sync over time has finally been debunked by a major scientific study. So if you find yourself coming on your period at the same time as your best friend, close relative or co-worker, it’s probably just a numbers game.
Period tracking and fertility app Clue recently partnered with the University of Oxford for what is thought to be the largest scientific study of its kind, surveying the responses of 1,500 women before narrowing them down to just 360 pairs, The Guardian reports.
Researchers then analysed three consecutive menstrual cycles, and found that there was a greater difference in period start dates at the end of the study than at the beginning for the majority of participants (273 out of 360 pairs).
‘It’s very unlikely that cycle syncing is a real phenomenon,’ Clue’s data scientist Marija Vlajic told The Guardian.
‘Menstrual syncing amongst the sample we had did not exist. We’ve also done some statistical tests and found that the difference in cycles actually grows,’ she added. ‘This doesn’t mean that pairs go out of sync – it means they were never in sync in the first place. It’s the nature of two mathematical series that keep repeating: the series will diverge as the numbers grow.’
Vlajic went on to explain that if we do notice some synchronisation, it’s just a simple matter of probability and numerical patterns.
‘There will be a time every six months, say, when your periods sync but that doesn’t mean the difference is getting smaller,’ she said.
‘I just think it’s information bias; our brains looking for patterns.’