Räta linjens ekvation och fetmaepidemin

Derivatan är poetiskt vacker, och y = kx+m är inte så dum den heller. Att via raka linjer dra ut trender fyrtio år i framtiden baserat på de senaste trettio årens data och inte ens studsa till inför slutsatsen att hela befolkningen någon gång kommer bete sig likadant är långt ifrån lika vackert. Faktum är att det är långt förbi skrattretande korkat, och redan gemene mellanstadielärare hade tillrättavisat elever som dragit sådana slutsatser.

Men nämn fetmaepidemi eller folkhälsa i din forskning, och källkritiken går alldeles ut genom fönstret - i stort sett varenda svensk tidning, bland dem Expressen, Aftonbladet, SvD och DN, har okritiskt publicerat TT-meddelandet. Sandy Szwarc har naturligtvis redan skrivit väl om ämnet - några citat:

Illustrating the nonsense inherent in mathematical extrapolations, for example, between 1947 and 1952, the number of television sets in American homes increased around 10,000%. Projected for the next five years would predict 40 sets per family! And if you want to be even sillier, begin with a year before television sets were available, and you can “prove” that each family will have 40,000 sets! Now, that’s an epidemic of television sets.
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The bell curve [över BMI] also isn’t corrected for age and the population is aging, significantly so since the 1950s and 1970s, especially in the babyboomer age group. Animals and the human species naturally gain weight with age, especially during middle age. As Dr. Friedman said, aging could notably contribute to the perception that weights in our population are increasing. [Szwarc citerar även Friedman angående hur mycket vikten i snitt ökat sedan 40-talet: 7-10 pund (~3-5 kilo).]

And then there are all of those modern advances that have helped children and adults to live longer, healthier lives, even while contributing to healthier average weights and heights among the population. Modern food production has improved, enabling more affordable food to feed more people. Compared to past generations and previous war times, fewer people are going hungry or facing food rationing or severe nutritional shortfalls, which had left more people underweight for their genes and skewed the population averages slightly downward. Our food and water are considerably safer today and have reduced by 100-fold the number of children and adults sick (and dying) with foodborne illnesses. Far fewer children spend their childhoods sick and fighting childhood illnesses, that have been eradicated just in recent decades. Most of us remember measles, mumps, chicken pox and polio among our classmates and siblings when we were younger. As recently reported, according to the CDC, before the introduction of the measles vaccine, alone, in 1963, “approximately 3 to 4 million persons had measles annually in the United States; approximately 400-500 died, 48,000 were hospitalized, and 1,000 developed chronic disability from measles encephalitis.”

And, of course, there are other possible iatrogenic factors, such as stress and prescriptions for anti-depressants and anti-anxiety medications that tripled between 1988 and 1999, most of which have been shown to increase weight, diabetes and auto-immune disorders. Smoking, which many used to help control weights, is down. Dieting, which since the 1970s has grown into a $61 billion/year industry in the U.S., can help to ratchet up weights if diets are repeated in rapid succession. And so on.