The adaptation, reliability and validity testing of the Estonian version of the Health Assessment Questionnaire’s Disability Index

The aim of our study was the adaptation of the Health Assessment Questionnaire’s Disability Index (HAQ-DI) for Estonia along with the assessment of its psychometric properties. The linguistic validation included phases of translation, back translation and testing on patients. Reliability and validity were tested on a sample of 50 rheumatoid arthritis patients by administering the HAQ-DI and the comparator instruments at two visits; disease activity and radiological stage were assessed. The participants were asked to comment on the questionnaires. The HAQ-DI was easily translatable into Estonian. It showed good test–retest reliability, internal consistency, and ability to discriminate between different levels of self-perceived severity. Comparison with the comparators and performed assessments demonstrated expected convergent and divergent validity. Still, the participants’ comments revealed issues disregarded during the adaptation process. We recommend the Estonian HAQ-DI for rheumatoid arthritis clinical studies and trials; some aspects of the adaptation process are highlighted for further discussion.