Psychometric properties of the Staffordshire Questionnaire for Adolescent Idiopathic Scoliosis (SQ-AIS): convergent validity, internal consistency and test-retest reliability.

Background
Adolescent Idiopathic Scoliosis (AIS) is a structural spinal deformity impacting health-related quality of life (HR-QoL). The Scoliosis Research Society-22 revised (SRS-22r) questionnaire is standard for HR-QoL assessment, though it has limitations in validity, reliability, and language appropriateness. To address these, the Staffordshire Questionnaire for Adolescent Idiopathic Scoliosis (SQ-AIS) was developed, covering six domains: general health, pain, function/activity, self-image/appearance, mental health, and intervention. Higher scores reflect better HR-Qo (scores are not attributed to the intervention section). The psychometric properties of SQ-AIS remain unexplored.
Aim
This study evaluated the SQ-AIS’s psychometric properties, specifically convergent validity, internal consistency, and test-retest reliability.
Method
A cross-sectional study was conducted with AIS patients at the International Schroth Scoliosis Therapy (ISST) Camp, a seven-day intensive scoliosis treatment held in Novi Sad, Serbia. Participants from two camps (November 2023–January 2024) were included. Convergent validity was assessed through correlations between SQ-AIS and SRS-22r scores at total and domain levels (Pearson’s/Spearman’s). Correlation categories were: very weak (<0.19), weak (0.2–0.39), moderate (0.4–0.59), strong (0.6–0.79), and very strong (≥0.8). Internal consistency (Cronbach’s α ≥0.7) and test-retest reliability (ICC, classified from poor <0.50 to excellent >0.90) were evaluated. Pre- and post-camp SQ-AIS scores were compared. Analyses were performed in SPSS 27.0, with ethics approval obtained.
Results
The cohort included 29 patients (79.3% female), mean age 18.2 years (SD=3.35). Thoracic curves ranged from 15° to 59° (median 40.14, IQR 21) and lumbar curves from 18° to 63° (mean 39.50, SD=13.96). SQ-AIS showed statistically significant correlations with SRS-22r across domains (0.325–0.779), with weaker correlations in function/activity (ρ=0.325), moderate in mental health (r=0.572), and strong in pain, self-image, and total scores (0.645–0.779). Internal consistency was high (α=0.772–0.919), and test-retest reliability was good to excellent (ICC=0.833–0.957), though moderate for the total score (0.557, CI -0.225 to 0.829) (Tab. 1).
Discussion and conclusion
SQ-AIS demonstrates strong reliability and validity, aligning with SRS-22r, particularly in pain and self-image domains. The function/activity domain showed weaker correlations likely because SRS-22r includes broader impacts, like financial strain and family effects, while SQ-AIS focuses on daily activities. The moderate test-retest reliability for the total SQ-AIS score may reflect lower post-camp scores (3.94 ± 0.39 vs 4.44 (0.40), see Tab.1) due to patients’ reassessment of HR-QoL after intensive treatment. SQ-AIS appears to be a valuable alternative to SRS-22r, capturing both stable and evolving aspects of AIS impact on HR-QoL.