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

PURPOSE: 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). PATIENTS AND METHODS: 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. RESULTS: 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. CONCLUSION: 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.