Validation of the Adapted Bariatric Quality of Life Index (BQL) in a Prospective Study in 446 Bariatric Patients As One-factor Model

Background: The Bariatric Quality of Life Index (BQL) was created and validated as a nine-factor model in 2005 for the measurement of quality of life (QoL) in patients before and after bariatric surgery.Even though the results were acceptable, the statistical structure of the test was very unclear.

Methods: A total of 466 patients were enrolled in an ongoing prospective longitudinal German study. The assessment took place preoperatively and at 1, 3,6, 9, and 12 months postoperatively. After that period, reevaluations were done on a yearly basis. In addition to demographic and clinical data, QoL data were collected using the BQL, the Short Form 12 (SF-12v2), the Gastrointestinal Quality of Life Index(GIQLI), and the Bariatric Analysis and Reporting Outcome System(BAROS; old version since the study started in 2001). Statistical parameters for contingency (Cronbach's a), construct and criterion validity (Pearson's r), and responsiveness (standardized effect sizes) were calculated. The data of the assessments conducted preoperatively and after 6 and 12 months were used for the validation.

Results: The factor analysis and the screeplot showed that a one-factor solution explained 45.37% of variance. The selectivity of the items ranged between 0.61 and 0.85, and Cronbach's a was 0.898. The measurements showed similar excellent results with the analysis of all measurement points. Pearson's test showed a good retest reliability (r = 0.9). The correlations with the SF-12 and the Moorehead-Ardelt I questionnaire(MA-I) were significant, while the correlation with the GIQLI was low. The results of the correlation with the excess weight loss(EWL) (0.45 and 0.49) and the BMI (-0.38 and -0.47) were good.

Conclusion: The BQL is a valid instrument and should be preferred over generic questionnaires as it provides better responsiveness.