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 A1-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 12.3% 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.