Development of a short version of the German subjective cognitive decline questionnaire (SCD-Q17): a principal component analysis approach to item reduction

Since it was shown that Alzheimer’s disease (AD) begins many years before the onset of symptoms with subjective cognitive decline (SCD), there has been increasing interest in the early clinical stages where disease-modifying drugs are expected to have the greatest benefit. However, at this early stage cognitive testing may yield unremarkable results, it is necessary to find a tool that can provide a simple and reliable indication of SCD as a part of a screening tool for AD in the general population. The German version of the 24-item Subjective Cognitive Decline Questionnaire (SCD-Q) with a dichotomous answer scale was tested, which then revealed some challenges. For this reason, an adaptation of the questionnaire was necessary. 360 participants completed the SCD-Q, all of whom were outpatients at a memory clinic. The most relevant subitems were identified by principal component analysis. This analysis focused on the self-perceived perspective of the decline. Results of the principal component analysis, consultations with experts and feedback from respondents were integrated into a short version of the SCD-Q with 17 items and a Likert scale – the SCD-Q17. The SCD-Q17 was sent to 100 participants of the original questionnaire for re-completion and, a new cut-off value was calculated by receiver operator characteristic (ROC) curves. The SCD-Q17 is a useful tool for the reliable detection of subjective symptoms, and thus may prompt more in-depth assessments of the underlying etiology. CogScreen has been retrospectively registered at clinical trials (NCT06191952).