by Philip Alcabes, Ph.D.
Last week, the Think About It blog’s Weekly Health Roundup (14 Dec.) moved too fast.
Our bloggers applauded the behavioral policing of NYC’s Bloomberg administration as a factor in two pieces of news: the decline in New York City’s child obesity prevalence and an increase in life expectancy.
The Dec. 14th TAI blog post specifically mentioned four Bloomberg-era innovations: bans on smoking in restaurants, bars, and parks; the ban on trans fats in restaurants; the requirement to post calorie counts at chain restaurants; and the new ban on the sale of sugar-sweetened beverages in large-size cups.
Our bloggers didn’t consider two big problems, though.
First, there has been no convincing evidence that any one of the Bloombergian innovations has led to a reduced rate of disease. The city’s Department of Health and Mental Hygiene has indeed made such claims – but they were based on circumstantial evidence. For instance, evaluators found that people who order lower-calorie options at fast-food restaurants say they had read the posted calorie counts (the NYC health commissioner, Thomas Farley, might well believe that such correlations are evidence of cause-and-effect relations – but intelligent people know better).
Second, the data don’t support the conclusion that obesity prevalence has declined, nor the inference that the increased life expectancy demonstrates reduced risks of dying.
The obesity data are based on what are called “serial cross-sections.” That is, investigators weigh and measure a bunch of children to determine the distribution of BMI, body-mass index. Two years later, they do the same to a new bunch of children. To find that the second batch contains fewer high-BMI kids than did the earlier group tells us nothing about whether the children who were obese the first time around have now slimmed down. Because we don’t know if the children in the first batch even appeared in the second batch, and no individual child is observed at multiple times to track BMI increase or decrease.
These data don’t allow us to conclude anything at all about whether children are getting fatter or slimmer.
And life expectancy, it’s important to know, is just an average age at death. Life expectancy in a population will go up if people live longer, which is the point of measuring life expectancy in the first place. But L.E. will also go up if more wealthy people move into a region (because wealthy people live longer than poor people). And it will go up simply if more older people move in (because adding 70- and 80-year-olds to the population makes the average age at death go up – even though nobody’s chances of dying have changed at all).
In fact, over a short term and with the high rates of in- and out-migration that NYC has, the most likely expectation for the longer life expectancy in NYC isn’t lower risk of dying – it’s that the wealthy have bought up properties that the lower and middle classes can no longer afford.
So there’s no reason to think that the trans fat ban, smoking bans, or big-cups-of-soda ban have made New Yorkers healthier. It’s more likely that Mayor Bloomberg has simply made the city more hospitable to the rich.
Which doesn’t seem to merit applause at all.
Philip Alcabes is a professor in the Adelphi University School of Nursing and director of the Public Health Program. He is an epidemiologist and has studied the history, ethics, and policy of public health.
