Fehlende Werte in der Somatisierungsskala des SCL-90-R durch „Listenfragen-Effekt”: Häufigkeit in verschiedenen Surveys und Vergleich unterschiedlicher Imputationsmethoden

Item non-response is a potential threat to the validity of study results. Taking the somatisation subscale of the SCL-90-R as an example, we hypothesise a specific response pattern (checklist-effect) that is characterised by symptom-free persons not checking the not at all-category. The present study analyses the extent and relevance of this postulated checklist-effect. Our data is derived from a survey of n = 228 blue-collar workers who previously had filed applications for medical rehabilitation benefits (A1-study), and two additional surveys as well. We defined the checklist-effect by the following response pattern: (1) at least one missing value and (2) at least one valid item response and (3) no not at all-responses. Occurrence of the checklist-effect in the three datasets differed widely. 75% of the responders in the Al-Study had complete data, 16.2% a postulated checklist-effect. Imputation of missing values under the assumption of a checklist-effect led to a reduction of missing data in the somatisation-subscale from 12.o% to 0.4%. Ignoring the checklist-effect would overestimate the symptom level. Possible explanations for the effect are discussed. However, the validity of this effect has yet to be proven via methodological studies.