In recent years, various authors have tried to develop a comprehensive explanation for the electoral success of extreme-right parties in Europe. While some authors stress individual-level factors (ethnocentrism, political cynicism, distrust), others stress macro-level variables (party strategy, electoral system). In this field of research cross-national survey data are often used to ascertain the strength of extreme-right parties and the motivation of those who vote for them. Hooghe and Reeskens question the external cross-cultural validity of these measurements, on the grounds of both response and measurement bias. Using the European Social Survey (29 observations) they find a huge diversity in the external validity of the data, with anything from 15 to 90 per cent of the electoral strength of the extreme-right party being covered in the survey. Using a multiple regression model, they identify survey response rate, voter turnout and the populist appeal of the party itself as possible causes for this selective under-representation. The only possible conclusion is that cross-national surveys do not succeed in establishing cross-cultural external validity for questions of extreme-right voting.