The Relationship between Confounding, Effect Modification and Ecological Bias
Wang Jianhua,Department of Epidemiology tTianjin Medical College ,Tianjin
Ecological bias is sometimes attributed to confouding by the group variable (ie, unit (or ecological analysis), or to risk factors associated with the group variable. Effect modification can lead to profound ecological bias. whet her or not the group variable or the effect modifier are independent risk factors. An extraneous risk factor need not be associated with the study variable at the individual level in order to produce ecological bias. Thus the conditions for the production of ecological bias by a covarite are much broader than the conditions for the production of individual level confounding by a covariate. Standardization or ecological control of variables responsible for ecological bias are generally insufficient to remove such bias.