Is the public sweet on sugary beverages? Social desirability bias and sweetened beverage taxes.

Social desirability bias has been documented in self-reported diet as well as in voting behavior, but not in regards to sweetened beverage consumption or sweetened beverage taxes. We find evidence that respondents in a mixed-mode opinion survey exhibit social desirability bias in both reported sweetened beverage consumption and beliefs about the health and economic benefits of sweetened beverage taxes. We do so in a study of 1704 adults residing in Seattle, Minneapolis, and the D.C. metro area. Phone respondents in our survey under-report sweetened beverage consumption by 0.63 beverages per week relative to web respondents (average web respondent consumption is 3.55 beverages per week). They also over-report their beliefs about the positive health and economic impacts of sweetened beverage taxes by 0.54 points in an 18-point index (average web respondent index score is 2.79). These differences are measured after we control for selection into survey mode by using matching methods, and we interpret them as occurring due to social desirability bias. In contrast to these findings, there is no modal difference in respondents' stated approval of sweetened beverage taxes, and so we conclude that this question is not subject to social desirability bias.