Longitudinal validity of the hemophilia caregiver impact measure

The hemophilia caregiver impact (HCI) measure is a 36-item self-report tool that has documented reliability and validity in a large cross-sectional study, but its longitudinal construct validity is unknown. This study's objective was to evaluate the responsiveness of the HCI to clinically important change, and to provide interpretation guidelines.

This web-based study invited 458 hemophilia caregivers involved in the HCI's validation study to provide follow-up data. Measures included the HCI, and a Likert item querying Global Assessment of Change (GAC) for caregiver burden. Responsiveness was estimated using anchor- and distribution-based methods. The anchor-based method computed the minimally important difference (MID) by computing the mean change separately for those who reported lesser or more caregiver burden on the GAC. The distribution-based method computed the Modified Standardized Response Mean (MSRM) separately for people who reporting reduced or increased burden as compared to the 'same' groups.

The study sample included 323 caregivers (71% response rate), with mean follow-up of 21.9 months. The HCI Burden Summary score and all negative-burden subscales but not the Positive Emotions subscale evidenced responsiveness to clinically important differences, showing statistically significant differences by transition group. The MIDs were relatively small mean changes over time (e.g., Burden Summary MID ranged from - 2.2 to 2.6, for reduced versus increased burden), and the MSRMs were small effect sizes. The Burden Summary score was equally sensitive to reduced versus increased burden (MSRM of - 0.32 and 0.35, respectively).

The HCI demonstrated longitudinal construct validity. The HCI shows promise for clinical hemophilia studies as a caregiver-based tool for evaluating treatments.