Summary: Although left-right items are a standard tool of public opinion research, there remains some difference of opinion on the optimal response format. Two disputes can be identified in the literature: (a) whether to provide respondents with a small or large number of answer categories and (b) whether or not to administer the response scale including a midpoint. This study evaluates the performance of the 101-, 11- and 10-point left-right scales. These scales not only speak to the two disputed aspects of measuring the left-right dimension but are also common instruments in public opinion research. Drawing on data from a split ballot multitrait multi-method experiment carried out in a methodological pretest to the German Socio-Economic Panel (SOEP), the analysis shows that the choice of a response format makes a difference in terms of data quality: The 101- and 10-point scales are plagued by method effects. Moreover, an application from electoral research illustrates that the choice of response formats affects substantive interpretations about the nature of the left-right dimension. Since all three scales perform about equally well in terms of the ease of administration, the findings suggest that the 11-point left-right scale should be used in survey research.

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