Internal consistency and criterion, convergent, and discriminant validity of the Start Back Screening Tool in a Colombian sample

Introduction: Low back pain (LBP) is a frequent reason for consultation, and one of the main causes of permanent work disability. Stratifying the risk of disability due to LBP allows the development of specific therapeutic interventions; however, such stratification requires valid and reliable instruments. Objective: To determine the internal consistency, as well as the convergent, discriminant, and criterion validity of the Start Back Screening Tool (SBST) questionnaire in a Colombian sample. Materials and methods: Quantitative scale validation study conducted in 68 adult patients with LBP who underwent a physical therapy intervention (10 sessions) between 2019 and 2020 in a clinic located in Chía, Colombia. Participants completed the SBST, the Numerical Pain Rating Scale (NPRS), and the Roland-Morris Disability Questionnaire (RMDQ) at three times: pre-intervention, post-intervention, and after 6 weeks of follow-up (without treatment). The internal consistency of the SBST was determined using Cronbach's alpha, omega, lambda-6, and greatest lower bound (GLB) coefficients. Regarding criterion and construct validity, correlations between the SBST and the NPRS and the RMDQ were assessed using the Pearson’s correlation coefficient. Finally, a repeated measures ANOVA was performed between the SBST mean scores obtained at the three moments in order to estimate its discriminant validity. Results: The internal consistency of the instrument, according to the different coefficients, ranged from acceptable to high (alpha=0.634; omega=0.648; lambda-6=0.664; GLB=0.780). Positive correlations were found between the SBST mean score (mean=3.824; SD=1.892) and the NPRS (r=0.257; p=0.035) and RMDQ (r=0.475; p<0.0010) mean scores, as well as significant differences between pre-intervention, post-intervention, and follow-up SBST mean scores (ANOVA: F=33.722; p<0.001). Conclusion: SBST is a valid and reliable instrument to classify the level of risk of poor prognosis in Colombian patients with LBP.