Inter-rater reliability of WHO ‘disability’ grading

The World Health Organization ‘disability’ grading system was introduced in 1960. It is mainly used as an indicator for early diagnosis or reporting. Disability grades are usually aggregated at national levels. Comparison of data with previous years or comparison of data between programmes may show that patients report earlier for treatment, alternatively, are diagnosed earlier, that is without, or with fewer ‘disabilities’. Despite its long and universal use as an epidemiological parameter, the WHO disability grading has not been the subject of reliability studies. In this study, three testers unfamiliar with the grading prior to the study each graded 65 (former) leprosy affected persons. The weighted kappa ranged from 0.87 to 0.89 (95% CI 0.73-1.00) for the highest score and from 0.90 to 0.96 (95% CI 0.90-0.99) for the EHF (Eye, Hand, Foot) score, indicating excellent reliability. The study shows that with limited training and little experience a high degree of reliability in grading ‘disabilities’ between testers is attainable.