Validity and reliability of the novel thyroid-specific quality of life questionnaire, ThyPRO

Abstract

Background: Appropriate scale validity and internal consistency reliability have recently been documented for the new thyroid-specific quality of life (QoL) patient-reported outcome (PRO) measure for benign thyroid disorders, the ThyPRO. However, before clinical use, clinical validity and test-retest reliability should be evaluated.

Aim: To investigate clinical ('known-groups') validity and test-retest reliability of the Danish version of the ThyPRO.

Methods: For each of the 13 ThyPRO scales, we defined groups expected to have high versus low scores ('known-groups'). The clinical validity (known-groups validity) was evaluated by whether the ThyPRO scales could detect expected differences in a cross-sectional study of 907 thyroid patients. Test-retest reliability was evaluated by intra-class correlations of two responses to the ThyPRO 2 weeks apart in a subsample of 87 stable patients.

Results: On all 13 ThyPRO scales, we found substantial and significant differences between the groups expected to have high versus low scores. Test-retest reliability was above 0.70 (range 0.77-0.89) for all scales, which is usually considered necessary for comparisons among patient groups, but below 0.90, which is the usual threshold for use in individual patients.

Conclusion: We found support for the clinical validity of the new thyroid-specific QoL questionnaire, ThyPRO, and evidence of good test-retest reliability. The questionnaire is now ready for use in clinical studies of patients with thyroid diseases.