More Errors In CDC Obesity Deaths Study
CDC’s Own Researchers Critique 'Loosey-Goose' Figure
Washington, DC – A simple math error that led to a gross overstatement by the Centers for Disease Control and Prevention (CDC) of the number of obesity related deaths in the U.S. is just the first of many flaws in the research, according to The Center for Consumer Freedom. The erroneous study has led to unwarranted alarm that obesity was set to surpass smoking as the number one preventable cause of death and an overhyped frenzy among policymakers and the media over the nation’s so-called "obesity epidemic."
A May 2004 article in Science magazine captured initial criticism of the study and highlighted disputes within the CDC that the data was weak. One critic said the figures were "loosey-goosey." Several epidemiologists at CDC and National Institutes of Health echoed this concern but declined to go public. "I don’t want to lose my job," one CDC staffer told the Science reporter.
This week, the CDC came clean and admitted that their March study suggesting that obesity caused 400,000 deaths each year was incorrect and may have overestimated by as much as 20 percent. Beyond this error, an analysis of the CDC’s flawed study by The Center for Consumer Freedom reveals that the data used to derive the 400,000 deaths figure was based on an even more flawed procedure used in 1999 by Dr. D.B. Allison of the University of South Alabama. "We used the same procedure reported by Allison et al. to estimate annual overweight-attributable deaths," wrote the CDC’s lead researcher.
Severe problems with the Allison study are alarming:
- Allison’s original study falsely presumed that "all excess mortality in obese people is due to obesity."
Due to the many factors that can influence mortality, Allison later conceded that, "Our estimates may be biased toward higher numbers due to confounding by unknown variables." A 1998 editorial in The New England Journal of Medicine accentuates this point: "Mortality among obese people may be misleadingly high because overweight people are more likely to be sedentary and of low socio-economic status."
- CDC researchers urged caution in use of Allison’s research and said methods led to bias
In a study submitted to the American Journal of Public Health prior to the 400,000 deaths study, a group of CDC researchers concluded: "Given the present knowledge about the epidemiology of obesity, and especially the impact of age on mortality risks associated with obesity, it may be difficult to develop accurate and precise estimates. We urge caution in the use of current estimates of the number of deaths attributable to obesity."
A second study by an overlapping team of CDC researchers found that Allison’s original study overestimated the total number of deaths by at least 17 percent -- and probably much more -- by not controlling for the influence of either age or sex. Writing in the American Journal of Epidemiology, they found: "Use of this [Allison’s] approach is contradicted by several published statistical papers, which show that such an approach can lead to bias…overestimation of deaths attributable to overweight and obesity in the U.S population is more likely than underestimation."
- Allison relies on exceptionally outdated risk assessments, some dating back to 1948 Both Allison’s and the current CDC studies rely on risk assessments based on six observational studies. The average start date of these studies was 1963 and the average end date was 1983. Consequently, the 400,000 figure assumes that our ability to treat high blood pressure, diabetes, heart disease, and other illnesses linked to obesity has not improved in a generation. Allison admits this is a problem. "When most of the cohort studies used were initiated," he writes, "there were fewer intervention strategies to reduce risk factors associated with obesity and fewer medical therapies for postponing death from obesity-related diseases." Yet no adjustment was made.
"The problems with this study go well beyond the simple math errors that the CDC admitted to," said Center for Consumer Freedom senior analyst Dan Mindus. "Since the CDC knowingly used refuted research as the basis for their false 400,000 figure, they have a public obligation to go back to the drawing board. Policymakers, public health groups and the media should immediately cease using this data and stop the ridiculous claim that obesity-related deaths rival those of smoking."
» View "An Epidemic of Obesity Myths".
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