Re: Source of cancer data

[RuthWeiner@AOL.COM]

In a message dated 12/26/01 12:06:49 PM Mountain Standard Time, hflong@postoffice.pacbell.net cites John Williams:



> > In most rigorous epidemiologic studies, such as case-control and
>
> > cohort studies, the basic unit of analysis is the individual. Each
>
> > individual is classified in terms of exposure and disease status.
>
> > However, in ecologic epidemiologic studies, the unit of analysis is
>
> > some aggregate group of individuals. 


I have no formal training in epidemiology.  However, there appears to me to be something wrong with this statement.


Am I wrong in thinking that epidemiology inherently is the study of groups?  Epidemiology reveals correlations, not causes of disease.  In general, every individual in a group studied does not get the disease being studied.  A case-control study is powerful because it provides much better control of confounding factors than an "ecological" study, but a case-control study is clearly still a study involving groups, not individuals.  If every member of a group exhibits the symptoms of a disease, and no member of the control group does, then one may have gone beyond epidemiology to find the cause of the disease.  


Ruth Weiner, Ph. D.

ruthweiner@aol.com