How is stigmatization affected by the "layering" of stigmatized conditions, such as serious mental illness and HIV?

Vignettes were used to examine the effect of labeling a person with two stigmatized illnesses, HIV disease and serious mental illness (schizophrenia). The additive model predicted that stigma associated with combined HIV and serious mental illness would resemble the simple sum of those for the two conditions. The discounting model predicted that the presence of serious mental illness would lead subjects to view the target individual as less responsible for infection, resulting in less stigmatization than given for HIV alone. Data collected from 244 participants at a public northeastern university supported the additive model. Stigmatization was highest in the group labeled with both HIV and serious mental illness, while stigmatization associated with someone with only HIV was less than those associated with someone with only serious mental illness. Possible explanations are discussed.