Sunday, November 25, 2007

A little public health

My professional interest is in public health, and one of the things I enjoy the most is trying to understand research and figuring out what it really means. There is a lot of research being bandied about in the news, etc., and often it is misinterpreted and used to prove someone's point.

One recent example that comes to mind is a discussion I've been having online with a fellow NaBloPoMo-er about breast cancer and abortion. There is a myth being perpetuated among the anti-abortion folks that having an abortion causes breast cancer. This myth is used -- obviously -- to convince women not to have abortions. While breast cancer is unfortunately very common, abortion does not cause breast cancer.

I looked in PubMed, which is an index of research articles published in reputable journals, and found a study done by a journal called the Lancet in 2004 that looked at data from53 studies and 83,000 women: a very large study (large is good for a study, small isn't always good)! What the researchers found is:
"Pregnancies that end as a spontaneous (meaning a miscarriage) or induced abortion do not increase a woman's risk of developing breast cancer. "
The researchers also found that:
"Collectively, the studies of breast cancer with retrospective recording of induced abortion yielded misleading results, possibly because women who had developed breast cancer were, on average, more likely than other women to disclose previous induced abortions."
There are 2 types of studies: prospective and retrospective. Prospective is when you take a group of people and follow them over time to see what happens. Retrospective is when you take a group of people who already have a disease, and ask them to look back at what happened to them in the past. The problem with the 2nd type of study is that when people have a disease and are asked to look back, they may not remember things correctly or accurately. Everyone forgets things, right?

For the purposes of this study, what this means is that that women who already had breast cancer who were asked to think back about whether they had an abortion or not, among other things. You can imagine that a woman who is seeing many doctors for breast cancer treatment is very likely to give her medical history over and over, and probably mentions things that she might not otherwise mention, like an abortion. If you had a group of women without breast cancer, and you asked them about their medical history, they might hide the fact that they had an abortion. So the breast cancer group may be more likely to disclose their abortion history than a non-breast cancer group. And this would affect the results of studies that ask women about their abortion history retrospectively.

So...if you've followed me this far... what the researchers are saying is that some studies that asked women with breast cancer to look back and reveal if they had abortions, initially showed results that indicated that abortion may lead to an increase in breast cancer... but after looking at these studies, researchers concluded that these retrospective studies were flawed (because the breast cancer patients were more likely to reveal their abortion history than women without breast cancer). Hopefully, this makes sense. If not, it's easy to see why there is so much confusion out there in the world about research!


nachtwache said...

Yes, makes sense. It's good to get facts straight or straighted :) Thanks.

BipolarLawyerCook said...

Good for you. Misinterpreted or underexplained stats drive me NUTS.