Content validity and test-retest reliability of a low back pain questionnaire in Zimbabwean adolescents

Background In Zimbabwe, a recent increase in the volume of research on recurrent non-specific low back pain (NSLBP) has revealed that adolescents are commonly affected. This is alarming to health professionals and parents and calls for serious primary preventative strategies to be developed and implemented forthwith. Early identification initiatives should be prioritised in order to curtail the condition and its progression. In an attempt to be proactive in minimising the prevalence of recurrent NSLBP, this study was conducted to evaluate the content validity and test-retest reliability of a survey questionnaire with the aim of proffering a valid and reliable questionnaire which can be used in non-clinical settings to identify adolescents with recurrent NSLBP in Harare, Zimbabwe and determine the possible factors associated with the condition. Methods The study was conducted in two parts. The first part assessed content validity of the questionnaire using four experts derived from academia and clinical practice. The second part evaluated the reliability of the questionnaire among 125 high school-children aged between 13 and 19 years in a test-retest study. Results Twenty-six (26) out of thirty questions in the questionnaire had an Item Content Validity index of 1.00, demonstrating complete agreement among content experts. Overall, the Scale Content Validity Index for the questionnaire was 0.97. Item completion for the reliability study was satisfactory. The questionnaire items had kappa values ranging from 0.17 (slight agreement) to 1 (perfect agreement). High levels of reliability were found for the questions on school bag use (k=0.94), sports participation (k=0.97), and lifetime prevalence (k=0.89). Conclusion Excellent content validity and slight to perfect test-retest reliability was found for the Low Back Pain (LBP) questionnaire. These results are comparable to findings of other studies evaluating the psychometric properties of LBP questionnaires. Cognisant of the limitations of the study, the results of this study suggest that the LBP questionnaire could be used in local studies investigating LBP among adolescents although questions enquiring on functional limitations and sciatica may need further consideration.