We Are All Keen For Great Information On The Weight problems Front – But Let’s Not Be Fooled By Shaky Statistics
Yesterday’s information that the prevalence of obesity amongst 2-five 12 months-old young children had decreased by a whopping 43 % created headlines across the country. The New York Instances announced on its site: “Obesity Fee for Younger Young children Plummets 43 Percent in a Decade.”
The considerably ballyhooed statistic derives from a review by researchers at Nationwide Center for Wellness Statistics, part of the Centers for Disease Handle and Prevention (CDC), which was published yesterday in JAMA.
The researchers employed information from a representative survey of the US population – the National Wellness and Nutrition Examination Survey (NHANES) — to examine trends in the prevalence of obesity in youngsters and grownups between 2003 and 2012.
While the media trumpeted the result, health pros hailed the news and interpreted it as a sign that we may ultimately be seeing the beginnings of a reversal in the upward trend in obesity in excess of past decades.
Actually, the JAMA paper reported the consequence in two-5 year-outdated young children as one particular end result in an all round image which showed no change in weight problems either in children and adolescents or in adults more than the 10-12 months time period.
Even so, few people bothered to search at the numbers in the paper that provided the basis for the dramatic reduce – or to assess how they should be interpreted.
This 1 variety was latched onto, taken out of context, and turned into a a lot far more solid reality than it has any correct to be. The authors themselves make a quantity of qualifications and cautions, but, of program, these did not make it into the headlines, or a lot of of the information stories.
Very first of all, the overwhelming information in the paper for the 10-year period display no change in obesity costs. And the paper’s conclusion does not highlight – in fact, does not even mention — the result in young young children. Rather, it reads in its entirety as follows:
“Overall, there have been no considerable alterations in weight problems prevalence in youth or adults between 2003-2004 and 2011-2012. Obesity prevalence stays higher and therefore it is crucial to proceed surveillance.”
The striking consequence comes from Table six.
Let’s seem at the data that gave rise to the dramatic obtaining. The third line down exhibits the final results for the group in query. For the 5 intervals for which data are presented, the prevalence of weight problems in the two-5 years age-group was: 13.9, ten.7, 10.one, 12.1, and eight.four %. Observe that the trend was decreasing in excess of the 1st 3 intervals but went up in the fourth interval before going down in the fifth.
If a single calculates the percent decline from 2003-2004 to 2009-2010 – rather than for the time period 2003-2004 to 2011-2012 – one particular obtains a much significantly less remarkable 14 percent rather than 43 %. In reality, researchers who use survey data like those presented in the JAMA paper are properly mindful that there are likelihood fluctuations in such data, and they are generally wary of seizing on short-term alterations inside of subgroups.
The authors are aware of this and state, “The assortment of the original stage can have an impact on the findings.”
In fact, due to the fact of their awareness that calculating the % change from 2003-2004 to 2011-2012 may be shaky, in a supplementary table they use information from all years to assess the trend from 2003 to 2012. This is a far more meaningful method due to the fact it uses all of the data. In boys the trend was not substantial – meaning that the alter was not various from what would be expected due to possibility. In girls, the trend just met the cutoff for statistical significance.
Discover also in Table six that the two-five 12 months age-group is a subgroup inside the 2-19 yr age grouping, which showed no hint of a modify in prevalence of obesity. Neither did either of the two other subgroups. This ought to also make us temper any weight we place on the 2-5 year age group.
In fact, the lower is not truly 43% — this variety is the end result of rounding the two percentages concerned (13.9 to 14 and eight.four to 8). If one particular had bothered to calculate the much more proper worth it is 39.6 percent, which could then be rounded to 40 percent – not 43 percent. But 43 percent is what was written in the press release and that is what just about each and every news organization went with.
So, if the authors did not highlight the 43 % in their published paper, how did it get catapulted into front-webpage information? By that indispensable instrument of modern science – the press release.
The CDC’s press release publicizing the results of the examine zeroed in on the result in younger kids:
“New CDC information demonstrate encouraging improvement in weight problems costs between 2 to five yr olds.”
“Though all round obesity rates stay unchanged, rates in younger children improve”
“The most current CDC weight problems information, published in the February 26 concern of the Journal of the American Medical Association, show a substantial decline in obesity between young children aged two to 5 many years. Obesity prevalence for this age group went from virtually 14 % in 2003-2004 to just more than eight percent in 2011-2012 – a decline of 43 percent – based mostly on CDC’s National Wellness and Nutrition Examination Survey (NHANES) information.”
What happened I consider is that, not remarkably, the researchers themselves and the publicity department at CDC determined to highlight this ray of hope in the otherwise bleak data.
This minor blip in the data could or might not be the beginning of a palpable trend in obesity rates. In the CDC press release, Tom Frieden, the head of CDC, cited other indications that obesity may be beginning to lower in youthful young children. But, as some informed commentators pointed out with regards to the JAMA paper, a single would want to see a lot more years of data ahead of putting also much excess weight on the drop in obesity charges in the 2-five 12 months age-group.
The authors state that, in see of the seriousness of the weight problems epidemic, it is critical to check charges of obese and weight problems in the U.S. population. No a single will argue with that. But we see from this review how a discovering can be taken out of context and pumped up.
What the 43 % consequence actually has to offer you is a lesson in how effortless it is to over-interpret statistics, specially when they seem to be to point in the wanted direction.
Geoffrey Kabat is a cancer epidemiologist at the Albert Einstein College of Medication and a contributing editor at STATS (Statistical Assessment Services) at George Mason University. He is the author of Hyping Health Dangers: Environmental Hazards in Day-to-day Daily life and the Science of Epidemiology.
How Credible Is CDC"s 43 % Decline In Obesity In Youthful Young children?
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