Vision and Quality of Life: Development of Methods for the VisQoL Vision-Related Utility Instrument

Abstract

Purpose: To describe the methods and innovations used in constructing the VisQoL, a vision-related utility instrument for the health economic evaluation of eye care and rehabilitation programs. Methods: The VisQoL disaggregates vision into six items. Utilities were estimated for item worst responses (the worst level for each item, with all other items at their best level) and VisQoL all-worst responses (all items at their worst level) using the time trade-off procedure. Time trade-off questions require people to imagine living a fixed number of years with a particular health condition and then indicate how many of those years of life they would be willing to trade to have perfect health. Where respondents indicated a health state was "worse than death" negative utilities were estimated. Time trade-off questions minimized the "focusing effect," which occurs if respondents discount the fact that all other aspects of health are at their best when answering questions, by using pictorial and verbal aids. Results: Item utilities were combined using a multiplicative model, and VisQoL model utilities placed on a scale where 0.00 and 1.00 represent full health and death, respectively. The VisQoL allows utilities to be calculated for a wide range of vision-related conditions. Conclusion: The 6-item VisQoL has excellent psychometric properties and is specifically designed to be sensitive to vision-related quality of life. It is the first instrument to permit the rapid estimation of utility values for use in economic evaluations of vision-related programs.

Patient-reported outcomes (PRO's) in glaucoma: a systematic review

“…34 The latter instruments should therefore not 42 Two types of instruments can be distinguished based on the scoring systems within our selected tools. Seven questionnaires have to be rated on a simple ordinal scale, while two instruments are preference based measures (ie, ViSQoL 43,44 and GUI 38 ) where all patients are asked to choose between different health situations (eg, perfect health vs worst possible health/death). However, none of them demonstrated statistically justified response scales.…”

“…Yet, further adaptation and testing could improve instruments with potential, such as the GQL-15, IMQ and the GSI [24][25][26][27][28] Within the QoL-measures, both the Glau-QoL and VisQoL had an extensive and theory based development process, but were generated and validated according to classical techniques. [43][44][45] Applying additional Rasch-analysis could strengthen their content and validity. The NEI-VFQ, which is a widely used QoL-instrument, has initially never been tested on its dimensionality, [35][36][37] which is a major flaw in its development.…”

Evaluation of a Vision-Related Utility Instrument: The German Vision and Quality of Life Index

“…The only vision-specific MAUI available currently is the 6-item Vision and Quality of Life Index (VisQoL), which was developed and validated specifically for vision-impaired populations. 2 To date, the VisQoL is available only in English, and has not been evaluated using modern psychometric theory, such as Rasch analysis, a form of item response theory. The VisQoL has been shown to perform well using classic test theory and its items were chosen based on item response theory different from the Rasch model.…”

“…The VisQoL has been shown to perform well using classic test theory and its items were chosen based on item response theory different from the Rasch model. 2,3 However, as the scale provides ordinal measurement of vision-related quality of life (VRQoL) based on its Likert scored descriptive system, and is summarized into a single score following conversion, Rasch analysis is useful not only in assessing the VisQoL's measurement properties, but also in transforming the ordinal score into an interval-level linear estimate. 4 Therefore, in our study, we determined the validity, reliability and measurement characteristics of the German VisQoL's descriptive system using Rasch analysis, and investigated the relationship between the severity of vision impairment, main causes of vision loss, and VisQoL measurement in a German sample of patients with and without vision impairment as well as healthy controls.…”

Moving Toward Scientific Measurements of Quality of Life

“…One might argue that the Peacock et al study 2 should also be singled out as more scientifically grounded than the others. The analyses described in their paper are complex and said to be driven by economic theory.…”