3 ms·

The report on nearly three million people found that those whose B.M.I. ranked them as overweight had less risk of dying than people of normal weight. And while

by kleiba 14y ago

The report on nearly three million people found that those whose B.M.I. ranked them as overweight had less risk of dying than people of normal weight. And while obese people had a greater mortality risk over all, those at the lowest obesity level (B.M.I. of 30 to 34.9) were not more likely to die than normal-weight people. I seriously don't understand this paragraph. Maybe it's because I'm a geek, but I was always under the impression that the risk of dying was 100% no matter which group you belong to. I don't understand what the author of the article is trying to convey here.

keithwinstein 14y ago
Most medical studies, including this one, summarize differences in risks by estimating a hazard ratio. A hazard function gives the conditional probability density of having an event at time T, given that no event has occurred at time t < T. (E.g. the probability that a hard drive first fails in its 14937th hour of operation, except that formally speaking we're talking about the probability density of failing not in an hour, but an infinitessimal instant.) A hazard ratio is the ratio of two hazard functions. Just as with hard drives, death is certain (eventually) but we can still prefer a hard drive with MTTF of 5 years vs. one with MTTF of 3 years.
YokoZar 14y ago
Without having read this study in detail, other possible things tend to muck up such studies. Suppose you define mortality as "chance of dying within a year" 1) People who start dying (eg by developing cancer) might take more than a year, and generally they lose weight when they do so. So even if obesity caused you to be more likely to get cancer and die, it wouldn't show up in this sort of data. 2) People who weigh less may be otherwise unhealthy for other reasons -- this doesn't imply that gaining weight would benefit them. In this sense weight is an effect of some other cause. 3) We may not be measuring "overweight" correctly -- scale weight is different from BMI which is different from body fat% which is different from body density which is different from body volume which is different from other things closely associated with "weight" (and specifically the stuff you gain/lose by eating)
sebcat 14y ago
FWIW, the JAMA article talks about mortality rate.
AndrewDucker 14y ago
It's usually the percentage chance of dying over the next year.

by kleiba 14y ago

keithwinstein 14y ago

Most medical studies, including this one, summarize differences in risks by estimating a hazard ratio. A hazard function gives the conditional probability density of having an event at time T, given that no event has occurred at time t < T. (E.g. the probability that a hard drive first fails in its 14937th hour of operation, except that formally speaking we're talking about the probability density of failing not in an hour, but an infinitessimal instant.) A hazard ratio is the ratio of two hazard functions. Just as with hard drives, death is certain (eventually) but we can still prefer a hard drive with MTTF of 5 years vs. one with MTTF of 3 years.

YokoZar 14y ago

Without having read this study in detail, other possible things tend to muck up such studies. Suppose you define mortality as "chance of dying within a year" 1) People who start dying (eg by developing cancer) might take more than a year, and generally they lose weight when they do so. So even if obesity caused you to be more likely to get cancer and die, it wouldn't show up in this sort of data. 2) People who weigh less may be otherwise unhealthy for other reasons -- this doesn't imply that gaining weight would benefit them. In this sense weight is an effect of some other cause. 3) We may not be measuring "overweight" correctly -- scale weight is different from BMI which is different from body fat% which is different from body density which is different from body volume which is different from other things closely associated with "weight" (and specifically the stuff you gain/lose by eating)

sebcat 14y ago

FWIW, the JAMA article talks about mortality rate.

AndrewDucker 14y ago

It's usually the percentage chance of dying over the next year.