Development and valuation of a preference-weighted measure in Age-Related Macular Degeneration from the Vision Impairment in Low Luminance (VILL) questionnaire – A MACUSTAR report

Objective

This study generates VILL-UI (Vision Impairment in Low Luminance - Utility Index), a preference-weighted measure (PWM) derived from the VILL-33 measure for use in patients with age-related macular degeneration (AMD), and valued to generate UK and German preference weights.

Methods

A PWM consists of a classification system to describe health; and utility values for every state described by the classification. The classification was derived using existing data collected as part of the MACUSTAR study, a low-interventional study on AMD, conducted at 20 clinical sites across Europe. Items were selected using psychometric and Rasch analyses, published criteria around PWM suitability, alongside instrument developer views and concept elicitation work that informed VILL-33 development. An online discrete choice experiment (DCE) with duration of the health state was conducted with the UK and German public. Responses were modelled to generate utility values for all possible health states.

Results

The classification system has 5 items across the three domains of VILL-33: reading and accessing information; mobility and safety; and emotional wellbeing. The DCE samples (UK: n=1004, Germany: n=1008) are broadly representative and demonstrate good understanding of the tasks. The final DCE analyses produce logically consistent and significant coefficients.

Conclusion

This study enables responses to VILL-33 to be directly used to inform economic evaluation in AMD. The elicitation of preferences from both UK and Germany enables greater application of VILL-UI for economic evaluation throughout Europe. VILL-UI fills a gap in AMD where generic preference-weighted measures typically lack sensitivity.