This is the text of a nonsensical piece of medical news about a surgical cut sometimes given during delivery.
Statistics are fun things. You can prove anything with them – to people who don’t pay attention. The mistake here is so basic and simple that one wonders what happened to down-to-earth common sense here.
The article opens with this statement: “Mothers who have an episiotomy during their first delivery are more likely to require the procedure in subsequent deliveries, according to researchers from Ben-Gurion University of the Negev and Soroka University Medical Center in Beersheba,” which should mean that two groups were compared and one scored higher.
In statistics, choosing an appropriate control group to compare your findings is crucial. It’s also the hardest thing to do. Say, you find a certain illness increased in a certain population. Then you want to know if that population changed or if the percentage of sick people changed. That is not so simple. Maybe they started eating differently, maybe there is more illness because fewer people died and it’s a sickness that comes with age. There are a million pitfalls to think of before drawing any conclusion. But our case here is not complicated at all (so wrong it is).
Of the women who needed a surgical cut during their delivery, 17.5 of those who needed that during their first delivery need one again during their second one. They claim that that is worrisome because the average for women who had none but needed one during the second time is only 3.1. The WHO recommends that it won’t exceed 10% (not as reported that it will be 10%).
Now the real story.
There is a small number of women that need such a cut at their first delivery. Of this 100% that needed it at their next delivery, 82.5% of them don’t need that again the next delivery. Their need falls from 100% to 17.5% Great progress.
Of course, you cannot compare this 17.5% to the local average to or general international norms because those are not compatible groups. Think of a Yemenite mother and a Dutch father. Great chance the child will be a bit big for the mother to birth.
If at the next delivery, only 17.5% needs another cut, that is almost 6 times better than the first time. That is not worrisome for the same couple at all. (Not a word if they checked that it was the same couple. They only discuss the mothers. A serious oversight.)
So the headline should proclaim good news. Mothers who have episiotomy in first delivery six times less likely to need one in next.