Background: The objective of the study was to translate and validate the questionnaire for the Obesity-Related Problems Scale (OP) in the Spanish language.
Methods: The translation-retranslation procedure and a pilot study were first conducted. Then, patients with morbid obesity who were on a waiting list to undergo bariatric surgery were selected. The construct validity of the OP scale was studied by means of exploratory and confirmatory factor analyses. Item convergent and divergent validity were examined. The internal consistency of the OP scale, floor and ceiling effects, concurrent validity, and known-group validation were also examined. The Short Form 36 and EuroQol-5D questionnaires were used to evaluate the concurrent validity.
Results: A total of 123 individuals took part in the field study. Factor analyses and the item convergent and divergent validity confirmed the homogeneity of the construct. The Cronbach's alpha coefficient was high (0.93), and floor and ceiling effects were small. Regarding the OP scale concurrent validity, the majority exceeded the correlation coefficient of 0.40, and all correlation coefficients were lower than the internal consistency of the OP scale. In relation to the known-group validation, significant differences were found in the OP mean scale according to body mass index (BMI) and age. Those patients with a higher BMI and younger patients reported more obesity-related problems.
Conclusion: These results confirm that this version of the OP scale has been translated and adapted correctly for the Spanish language and that it fulfils the psychometric properties required for these instruments.