Saturday, September 12, 2009
From the Archive: Value of learning empirical skills
Conventional wisdom holds that breastfeeding is vastly superior to bottle feeding. The superiority of breast milk is supposedly supported by scientific evidence. Upon closer examination, though, the evidence does not appear that overwhelming. Why?
most of the claims about breast-feeding’s benefits lean on research conducted outside the lab: comparing one group of infants being breast-fed against another being breast-fed less, or not at all. Thousands of such studies have been published, linking breast-feeding with healthier, happier, smarter children. But they all share one glaring flaw.The article continues to describe some very clever ways researchers have attempted to tease out the "true" effects of breastfeeding. Economists call these types of clever approaches "identification strategies", and a significant share of graduate training in labor economics consists of learning how to come up with these kinds of clever strategies.
An ideal study would randomly divide a group of mothers, tell one half to breast-feed and the other not to, and then measure the outcomes. But researchers cannot ethically tell mothers what to feed their babies. Instead they have to settle for “observational” studies. These simply look for differences in two populations, one breast-fed and one not. The problem is, breast-fed infants are typically brought up in very different families from those raised on the bottle. In the U.S., breast-feeding is on the rise—69 percent of mothers initiate the practice at the hospital, and 17 percent nurse exclusively for at least six months. But the numbers are much higher among women who are white, older, and educated; a woman who attended college, for instance, is roughly twice as likely to nurse for six months. Researchers try to factor out all these “confounding variables” that might affect the babies’ health and development. But they still can’t know if they’ve missed some critical factor. “Studies about the benefits of breast-feeding are extremely difficult and complex because of who breast-feeds and who doesn’t,” says Michael Kramer, a highly respected researcher at McGill University. “There have been claims that it prevents everything—cancer, diabetes. A reasonable person would be cautious about every new amazing discovery.”
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