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> and some studies suggest that those who sit all day live around two years less than those who are more active. Considering that truly unhealthy and sick peop

> and some studies suggest that those who sit all day live around two years less than those who are more active. Considering that truly unhealthy and sick people (who will soon die) probably sit more then they stand, if you remove those people from the dataset, wouldn't the interpretation become that sitting is actually extremely beneficial for the average person who will end up outliving a non-sitter person by several years?

lambda 13y ago
The studies most often cited to support this finding are studies of London bus drivers vs conductors (ticket takers) on the double decker London busses. They tend to be from similar socioeconomic backgrounds, start at similar young ages, and so on, controlling for many confounding factors, but the drivers spend all day sitting, while the conductors spent most of the day on their feet. However, when trying to find the actual study to see if they had controlled for any pre-existing conditions, I found this paper: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1008580/pdf/brjindmed00119-0013.pdf http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1008580/pdf/brji... which seems to indicate that in fact, people of heavier builds were more likely to become drivers than conductors, and conductors with heavier builds were more likely to switch to becoming drivers. So actually, it seems that the original study may be flawed, in the way you describe. While it did study people from a young and healthy age, it hadn't considered pre-existing weight or genetic differences between drivers and conductors, and it looks like that may actually play a substantial role in the difference in findings.
yetanotherphd 13y ago
No, you can't just reverse the causal effect by guessing the bias caused by reverse causality :-) If what you say is true (studies tend to try to account for these things, e.g. they can show that the effect of sitting exists even after accounting for exercise/activity on the job) then the correct interpretation is that we don't know the causal effect.

lambda 13y ago

The studies most often cited to support this finding are studies of London bus drivers vs conductors (ticket takers) on the double decker London busses. They tend to be from similar socioeconomic backgrounds, start at similar young ages, and so on, controlling for many confounding factors, but the drivers spend all day sitting, while the conductors spent most of the day on their feet. However, when trying to find the actual study to see if they had controlled for any pre-existing conditions, I found this paper: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1008580/pdf/brjindmed00119-0013.pdf http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1008580/pdf/brji... which seems to indicate that in fact, people of heavier builds were more likely to become drivers than conductors, and conductors with heavier builds were more likely to switch to becoming drivers. So actually, it seems that the original study may be flawed, in the way you describe. While it did study people from a young and healthy age, it hadn't considered pre-existing weight or genetic differences between drivers and conductors, and it looks like that may actually play a substantial role in the difference in findings.

yetanotherphd 13y ago

No, you can't just reverse the causal effect by guessing the bias caused by reverse causality :-) If what you say is true (studies tend to try to account for these things, e.g. they can show that the effect of sitting exists even after accounting for exercise/activity on the job) then the correct interpretation is that we don't know the causal effect.