Kilian Hasselhorn

• Ambulatory assessment (AA) is becoming an increasingly popular research method in the fields of psychology and life science. Nevertheless, knowledge about the effects that design choices, such as questionnaire length (i.e., number of items per questionnaire), have on AA participants’ perceived burden, data quantity (i.e., compliance with the AA protocol), and data quality is still surprisingly restricted. The aims of this dissertation were to experimentally manipulate aspects of an AA study’s sampling strategy - sampling frequency (Study 1) and questionnaire length (Study 2) - and to investigate their impact on perceived burden, data quantity, and aspects of data quality in three papers. In Study 1, students (n = 313) received either 3 or 9 questionnaires per day for the first 7 days of the study. In Study 2, students (n = 282) received either a 33- or 82-item questionnaire 3 times a day for 14 days. Paper 1 described that a higher sampling frequency (Study 1) led to a higher perceived participant burden, but did not affect other aspects of data quantity and quality. Furthermore, a longer questionnaire (Study 2) did not affect perceived participant burden or data quantity, but did lead to a lower within-person variability, and a lower within-person relationship between time-varying variables. Paper 2 investigated the effects of the sampling frequency (Study 1) on careless responding by identifying careless responding indices that could be applied to AA data and by extending the multilevel latent class analysis model to a multigroup multilevel latent class analysis model. Results indicated that a higher sampling frequency did not affect careless responding. Paper 3 investigated the effects of questionnaire length (Study 2) on (the relative impact of) response styles by extending the item response tree (IRTree) modeling approach to a multilevel data structure. Results indicated that a longer questionnaire led to a greater relative impact of RS. Although further validation of the results is essential, I hope that future researchers will integrate the results of this dissertation when designing an AA study.