Interaction analysis of question–answer sequences from a telephone survey shows that so-called mismatch answers, i.e. answers that do not correspond to the required answering format, are the most frequently occurring problematic verbal behavior. They also are likely to trigger suggestive interviewer probing. Explanations for the occurrence of mismatch answers concern cognitive and conversational factors. In both a non-experimental and an experimental study it was found that questions with formal response alternatives yield more mismatch answers than questions with colloquial response alternatives (i.e., words that are frequently used in ordinary conversations). Effects of the wording of questions were only found in the non-experimental study, indicating that formal question wording yields fewer mismatch answers than colloquial question wording. The findings suggest that, especially in case of questions that are formulated as agree–disagree opinion assertions, the chance of mismatch answers is highly reduced when colloquial response alternatives are used.