When designing a Web questionnaire, various HTML input elements can be used to register the respondent’s answers. Two of these input elements, radio-buttons and drop-down boxes, can be regarded as technically equivalent since they serve the same purpose: they both allow to select one answer from a list of response options. However, these input elements are dissimilar from each other in many respects and there is reason to believe that some people are less familiar with drop-down boxes. By means of two experiments, this study evaluates the effect of the two response formats on data quality. Lower data quality was expected in the drop-down boxes condition than in the radio-buttons condition. The data showed that a slight preference for radio-buttons might be justified, although both response formats have benefits and drawbacks. Consequently, the choice between these response formats is not self-evident and needs to be guided by other considerations such as sample composition and survey design.