Psychometric Analysis of the Patient-Reported Hypoparathyroidism Symptom Diary Symptom Subscale Using Data from Two Clinical Trials.

Abstract

The hypoparathyroidism symptom diary (HypoPT-SD) is a disease-specific patient-reported outcome (PRO) tool comprising a 7-item symptom subscale, a 4-item impact subscale and 1-item anxiety, and sadness or depression components. This analysis assessed the psychometric properties of the HypoPT-SD symptom subscale scores using data from two open-label, single arm, Phase 4 studies (Study 402 and Study 404). Eligible patients were aged 18 years or older with a confirmed diagnosis of hypoparathyroidism. All patients received recombinant human parathyroid hormone (1-84) during the analysis period. Scores were recorded at baseline, and at months 6, 30 and 36 (end of treatment [EOT]) in Study 402, and at baseline and week 52 (EOT) in Study 404. The structure of the HypoPT-SD Symptom subscale was analyzed by measuring correlations between pairs of item scores; internal consistency and reliability were evaluated using Cronbach's coefficient α; test-retest reliability was assessed using intraclass correlation; and construct validity was determined by performing correlational analyses between scores recorded using the HypoPT-SD and those for other conceptually similar PRO tools. A total of 60 patients were included in the analysis. Inter-item pairwise correlations were strong for all but 5 of the item pairs analysed. Cronbach's α values for the HypoPT-SD Symptom subscale were 0.88 using data from Study 402 and 0.92 using data from Study 404. In general, the HypoPT-SD Symptom subscale scores had moderate or strong correlations with scores recorded using PRO tools. Intraclass correlation coefficients exceeded 0.70 using test-retest data from all patients in Study 402 and from a subgroup of patients with stable disease from Study 404. This analysis demonstrated the test-retest reliability, internal consistency and construct validity of the HypoPT-SD using data from longitudinal prospective studies and supports the use of the HypoPT-SD in future clinical studies.