Preparing the survey questionnaire is a major challenge in research. The questionnaire must meet certain requirements in order to provide quality data for further analysis. I chose the content of the questionnaire to be the main focus of my diploma paper. The basic assumption of independence of the questionnaire is that all respondents have the same understanding of the questionnaire. The boldness of this assumption creates a need for (pre-)testing the survey questionnaires. In my diploma paper, I tested the General Health Questionnaire (GHQ-28) using the cognitive interview method. I applied the technique of explanatory supplementary questions, and the technique of proposing definitions, using two approaches – the personal cognitive interview, and an online cognitive interview. The different research approaches can yield different results, as has been confirmed over the course of writing this paper. The results show that both of the hypotheses can be confirmed. The online cognitive interview is more limited in terms of the choice of techniques, the degree of the cognitive interviewer’s active involvement affects the different outcomes of the cognitive interview. When compared to the online interviews, more issues were identified with personal cognitive interviews.