Kellner's Symptom Questionnaire, a Highly Sensitive Patient-Reported Outcome Measure: Systematic Review of Clinimetric Properties

Introduction: Patient-reported outcomes (PROs) are of increasing importance in clinical medicine. However, their evaluation by classic psychometric methods carries considerable limitations. The clinimetric approach provides a viable framework for their assessment. Objective: The aim of this paper was to provide a systematic review of clinimetric properties of the Symptom Questionnaire (SQ), a simple, self-rated instrument for the assessment of psychological symptoms (depression, anxiety, hostility, and somatization) and well-being (contentment, relaxation, friendliness, and physical well-being). Methods: The PRISMA guidelines were used. Electronic databases were searched from inception up to March 2019. Only original research articles, published in English, reporting data about the clinimetric properties of the SQ, were included. Results: A total of 284 studies was selected. The SQ has been used in populations of adults, adolescents, and older individuals. The scale significantly discriminated between subgroups of subjects in both clinical and nonclinical settings, and differentiated medical and psychiatric patients from healthy controls. In longitudinal studies and in controlled pharmacological and psychotherapy trials, it was highly sensitive to symptoms and well-being changes and discriminated between the effects of psychotropic drugs and placebo. Conclusions: The SQ is a highly sensitive clinimetric index. It may yield clinical information that similar scales would fail to provide and has a unique position among the PROs that are available. Its use in clinical trials is strongly recommended.