Reliability and validity of the Spinal Appearance Questionnaire (SAQ) and the Trunk Appearance Perception Scale (TAPS)

BACKGROUND: The Spinal Appearance Questionnaire (SAQ) and the Trunk Appearance Perception Scale (TAPS) are questionnaires that mostly rely on drawings to assess scoliosis patients’ subjective viewpoints on their trunk deformity. Our aim was to perform an in-depth assessment of the psychometric quality of both measures, the SAQ (version 1.1) and TAPS, and compare them to provide practical recommendations. METHODS: Web-based survey study with 255 patients suffering from idiopathic scoliosis (age 30.0 ± 16.7 years, Cobb angle 43.5 ± 20.9°) and 189 matched healthy control individuals. Participants answered a broad set of validated questionnaires including SRS 22-r, PHQ-9, PANAS, FKS, WHO-5, BFI-S, and PTQ. We calculated reliability (Cronbach’s α, test–retest correlations) as well as factorial, convergent, divergent, concurrent, and discriminant validity. RESULTS: Reliability was high (Cronbach’s α ≥ .86; test–retest r ≥ .80), except for test–retest correlation of the SAQ Expectations scale (r = 0.67). Both the SAQ and TAPS measures showed clear factor solutions, indicating factorial validity. High correlations with theoretically related measures (e.g., SRS 22-r, overall stress, Cobb angle) indicated convergent validity. Moderate correlations occurred with concurrent criteria such as mood, depression, body dysmorphic disorder, and well-being. The matched-pair analysis revealed strong evidence for discriminant validity (Cohen’s d > 2 for SAQ total score and TAPS). Subgroup analyses showed that patients with more severe Cobb angles (≥ 40°) and those ≥ 46 years of age had significantly worse SAQ and TAPS scores. CONCLUSION: We recommend using the TAPS for future clinical workups and research, as it is much shorter and revealed slightly higher psychometric quality in comparison to the SAQ. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s13018-018-0980-1) contains supplementary material, which is available to authorized users.