The ascendance of the left in Latin America has sparked new interest in the politicization of social class. What factors should scholars consider in choosing and constructing measures of social class in survey research? To what degree can measurement affect results? This article evaluates several common measures in terms of validity and reliability. It then shows that alternative measures produce strikingly different results when examining class voting in Venezuela's 2006 presidential election. Simple measures of household income or wealth, which fare poorly in validity assessment, suggest minimal levels of class voting. Various socioeconomic scales that also incorporate data on education and, in some cases, weights for household composition, suggest very high levels of class voting. The article provides guidelines for evaluating measures and illuminates the debate on class voting in Venezuela. Scholars have reached contradictory conclusions while using different measures, but the decisive role of measurement has gone unrecognized.