Validity and reliability of the German version of the shortened thyroid-specific quality of life questionnaire (ThyPRO-39de)

Abstract

Objectives Validation of a German version of the ThyPRO-39 questionnaire for quality of life (QoL) in patients with benign thyroid diseases. Design Internal consistency, retest reliability, and validity were to be assessed in a test-retest study. Methods The ThyPRO-39 was translated based on standard methodology. A sample of 98 patients with benign thyroid diseases was tested with the ThyPRO-39de and the generic EuroQol 5D-5L. Forty-four patients with stable symptoms after 2 weeks formed the repeated measures sample. Cronbach’s alpha was calculated for the ThyPRO-39de composite score and for each disease-specific scale. Intraclass correlations between the original and the repeated measures sample were calculated for each scale as well as Pearson correlations between various ThyPRO scales and the EuroQol. T-tests were used to test for differences in the goiter and hyperthyroid symptom scales between relevant patient groups and other patients. Results Internal consistency was between satisfactory and good, except for two scales (tiredness and cosmetic complaints/appearance). The test-retest correlation was between 0.62 and 0.8 for most scales, but below 0.5 for two scales (tiredness and impaired social life). There were significant correlations between the EuroQol index score and most aspects of the ThyPRO-39de. Only the hyperthyroid symptoms scale was specific for the relevant patient group (Graves’ disease). Conclusion The ThyPRO-39de may be recommended for use in clinical and research settings, especially with regards to the composite score. However, the underlying thyroid disease should always be kept in mind when interpreting the test results. A larger sample would be needed to implement further improvements.