The Three-Step Test-Interview (TSTI) is an instrument for pretesting a self-completion questionnaire by observing actual instances of interaction between the instrument and respondents (the response process). Because this process mainly consists of cognitive processing (‘thinking’) and is therefore hidden from the observer, (concurrent) think aloud is used as a technique for making the thought process observable. The productivity of the TSTI in identifying problems in questionnaires was assessed in three consecutive pilot studies. A manual for the application of the TSTI is appended
