Re: U.S life expectancy
Sorry, epidemiology is the study of who has what diseases, and where. If a health department gets a report of a kid with e. coli they won't think much of it. If they get five reports in a week, or any unusual amount then an epidemiologist would go out and interview all five or fifty to try to determine the link between them.
On a bigger scale epidemiologists prepare the reports on how many people in the nation die of lung cancer, colon cancer, breast cancer, heart disease, etc. Then try to determine the links between them. As our obesity goes up it seems that all of those other things do also.