Sunbathing and babies
The Herald (from the Daily Mail)
A sunshine break is the perfect way to unwind, catch up on your reading and top up that tan.
But it seems a week soaking up the rays could also offer a surprising benefit – helping a woman have a baby.
Increased exposure to sunshine could raise the odds of becoming a mother by more than a third, a study suggests.
If you read StatsChat regularly, you probably won’t be surprised to hear the study had nothing to do with either holidays or sunbathing, or fertility in the usual sense.
As the story goes on to say, it was about the weather and IVF success rates. The researchers looked for correlations between a variety of weather measurements and a variety of ways of measuring IVF success. They didn’t find evidence of correlations with the weather at the time of conception. As they said (conference abstract, since this isn’t published)
When looking for a linear correlation between IVF results and the mean monthly values for the weather, the results were inconsistent.
So, following the ‘try, try again’ strategy they looked at weather a month earlier
However, when the same analysis was repeated with the weather results of 1 month earlier, there was a clear trend towards better IVF outcome with higher temperature, less rain and more sunshine hours.
It helps, here, to know that “a clear trend” is jargon for “unimpresssive statistical evidence, but at least in the direction we wanted”. That’s not the only problem, though. Since these are honest researchers, you find the other big problem in the section of the abstract labelled “limitations”
Because of the retrospective design of the study, further adjusting for possible confounding factors such as age of the woman, type of infertility and indication for IVF is mandatory.
That is, their analysis lumped together women of different ages, types of infertility, and reasons for using IVF, even those these have a much bigger impact on success than is being claimed for the weather.
I don’t have any problem with these analyses being performed and presented to other consenting scientists who are trying to work out ways to improve IVF. On the other hand, I’m pretty sure the Daily Mail didn’t get these results by reading the abstract book or sitting through the conference. Someone made a deliberate decision to get publicity for this research, at this stage, in a form where all the cautionary notes would be lost.
Thomas Lumley (@tslumley) is Professor of Biostatistics at the University of Auckland. His research interests include semiparametric models, survey sampling, statistical computing, foundations of statistics, and whatever methodological problems his medical collaborators come up with. He also blogs at Biased and Inefficient See all posts by Thomas Lumley »
People tend to be healthier in body and mind during summer, seasonal affectation disorder subsides, so rays hitting the skin is probably only part of the equation regarding fertility.
Testicular ambient temperatures would rise in summer though, whereas keeping the goulies cool, improves fertility. Hmmmm.
Just did some googling and found this:
http://www.nzherald.co.nz/nz/news/article.cfm?c_id=1&objectid=11235292
It may be the relaxed and happy times the Christmas-New Year holiday brings, with new figures showing September 28 – nine months later – is the most common birthday in New Zealand.
Statistics New Zealand has analysed birth data from 1980 to 2013 and has come up with the most common days for New Zealanders to be born on.
The 10 most common birthdays of 366 days all fall between September 22 and October 4 – nine months after the Christmas-New Year holiday period.
Statistics NZ senior demographer Kim Dunstan said the pattern for births in New Zealand was similar to the pattern for births in the United States.
“September and October are the most common months for birthdays with the 30 most common birthdays all appearing in the 38-day period from 12 September to 19 October,” he said…..
To me this same pattern in the northern hemisphere would indicate that Xmas break increases fertility, not sunshine.
The period of pre xmas stress, then followed by flopping down for the next few weeks, would initiate a high fertility cycle in the body….much like stressing a plant can induce flowering…. would be my call on this one.
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10 years ago
I didn’t mention it, but they did also look at season and didn’t find a relationship. I’m a bit surprised it’s possible to find a relationship with sunshine but not with season in Belgium, but one of the disadvantages of working with conference abstracts is that they usually don’t have enough information to assess the research. Of course, that’s one reason not to do the publicity at the conference-presentation stage.
10 years ago