[Cognitive interviewing - a tool to develop and validate questionnaires]

Questionnaires concerning subjective health status are an important element of rehabilitation research. The appraisal of the quality of these instruments mostly relies on quantitative psychometric analyses. However, these analyses do not explicitly reveal whether or how respondents understand questionnaire content. Over the past few years cognitive interviewing has been increasingly used in questionnaire design and validation. It serves to identify potentially problematic questions, ambiguities and difficulties which could lead to unintended answers. It analyses whether the answers given by respondents represent the intended meaning of the question. Findings derived from cognitive interviewing serve to improve new and further validate well-established questionnaires.The 4-stage model of the survey response process by Tourangeau provides a conceptual basis for cognitive interviewing. The 2 most prominent methods of cognitive interviewing are think aloud and verbal probing. Various authors give recommendations on executing cognitive interviews but almost no recommendations exist on the -indications of the different methods.Potential applications of cognitive interviewing go beyond questionnaire design and improvement. Due to its origin in cognitive science it can also be used to resolve substantive questions, e. g. concerning reasons for discrepancies between the results of 2 different methods of measuring change.