According to an article in the current Journal of Health Politics, Policy, and Law, public opinion polls on health reform are at best incomplete and at worst misleading due to a systematic bias in non-responses.  Authors Berinsky and Margolis argue that, in the context of the healthcare debate at least, non-responses (e.g., answers like “Don’t know”) are more likely to come from individuals of lower socioeconomic status, and that “these same individuals who are victims of resource inequalities are natural supporters of the welfare state and, therefore, are more likely to back health care reform.”
The authors write that, to ensure full representation of views, nonresponses should not be ignored. Instead, the analysis “should incorporate information from respondents’ answers to other questions on the survey to understand what they might have said had they answered the question.”
Imputing the views and attitudes of non-respondents is a generally acceptable method for removing bias, provided it is done carefully using suitable assumptions. Berinsky and Margolis use income as the predictive variable. According to their analysis, for example, people making less than $30,000 annually are more likely to support health reform than those making more than $100,000.