<P> A final key part of the theory is the persistence of resource disparities that perpetuate unequal health outcomes, despite intervening mechanisms that may otherwise appear to improve health status . An example of this is the Pap smear for cervical cancer screening . Since the development of the Pap smear in the 1940s, a disparity has existed in utilization of this screening test given differences in resources mentioned above . Another example is the polio vaccine . Prior to the vaccine, polio could afflict people of all socioeconomic classes . Once the vaccine became available, it was primarily accessible by those who possessed the resources to obtain it . We also see an example of this in colorectal cancer, in which the variable diffusion has role in the theory; in which diffusion has reduced mortality, but not enough to eliminiate SES inequalities as seen in Wang et al. 2012 . </P> <P> These examples demonstrate how intervening mechanisms, e.g., the Pap smear and the polio vaccine, did not decrease health disparities given that certain groups possessed resources to access them and others did not . </P>

Are defined as the immediate causes of a given social problem