Liars, Damned Liars and Statistics
I was asked to comment on an item in the news showing 13 celebrities who had babies after the age of 40 (“and looked damn good doing it”). If this is so, the writer asks, why do fertility doctors incessantly talk about biological clocks and the importance of age? Indeed, the journalist herself describes any mention of age & fertility as mere “blather,” offering instead for her readers to think of age as “just a number.”
I think the message of this article is serious matter not only because it is misleading in potentially dangerous ways but also because it is based on a fundamental misuse of numbers.
To cut to the chase: what would the message be if the focus of the article had been on 13 Powerball lottery winners? Would we say that it’s a great idea to go out and buy a ticket for the lottery, in lieu of saving for the future? To bring it closer to home: what would the message be if the article profiled 13 women who had babies at the age of 50? Would it then be justifiable to conclude that 50 is the new 30?
But, of course, we know that this proves nothing. What really is important is not the number in the group that has been successful – in math, we would call them the numerator – but the total number of women their age who are trying to conceive – here, the denominator. So if we want to know what the LIKELIHOOD is of a woman having a baby after 40 (presumably, with her own eggs and with no treatment of any kind), we need to know how many were trying as well as how many are successful. That is, we need a denominator as well as a numerator. In this way we arrive at a statistical reference point, and we can do that for each age.
We can use the odds of winning the Powerball as an example. I lift them here from the NY Times:
The odds of hitting the jackpot are one in 292.2 million, which are really, really bad odds. Consider this:
- If you printed out the name of every United States resident on individual pieces of paper, put them in a giant bowl and selected one at random, the odds of picking the President are not far from the odds of winning the Powerball.
- The odds of being struck by lightning this year are one in 1.19 million, making it about 246 times more likely than winning the Powerball jackpot.
- With an estimated one in 12,500 chance, an amateur golfer is about 23,376 times more likely to make a hole in one.
Notice that the chances are always explained as “one in ….” So if the NY Times profiled the 86 winners of the Powerball since 2003, we would not jump to the conclusion that buying a ticket makes sense. Using the statistics as we understand them, those 86 winning tickets represented, as a group, some 25 billion tickets that were not winners.
Age & Fertility
Of course, no one would suggest that the odds of a woman over 40 having a baby are as dismal as the odds of winning the Powerball. Fortunately, they are in fact in a different universe of math, and much more hopeful. But the point is that using numerators to prove a point is a grave error and cannot prove anything. In fact, if age is just a number, let’s see if the writer can send us a follow up on celebrity women over 50 having babies (with their own eggs, please).
This slide, copied from a classic article in the New England Journal of Medicine, shows what the actual trend is. As is clear, age is not just a number, and the biological clock is no blather.
We should use articles like this to learn lessons, and not just about math or biology. First and foremost is that the media can be unkind to women. Articles like this one try to portray doctors as clueless about real life. In doing so, what they really do is give many women a false sense of security about their own life choices. Of course many women – and not just celebrities! – have no reproductive difficulties well into their 40s. That’s indisputable. But what salve would this journalist have for the legions of women (remember the denominator) who missed the chance to ever have a biological child because they truly believed that “age is just a number”? We cannot just wish away biology.
Secondly, the many lifestyle magazines that portray celebrities having twins at advanced ages forget to tell us that many (if not most) of them have used egg donors. Of course, that’s partially because it’s nobody else’s business. But when women are inundated with these stories and then must confront the news that their own clock has run out of time, who is to blame? To my mind, it is the irresponsible journalists who like nothing more than indicting the “fertility industry” for harping on biological truths.
Finally, we cannot reverse millennia of human evolution by making a wish. Forty may be the new thirty in fashion, lifestyle and overall health. But no one has yet figured out how to restore the fertility potential of a thirty year old woman to a forty year old woman. So until that happens, let’s say it like it is: if delayed childbearing is part of your life plan, be smart. Freeze your eggs as early as you can.