Introduction
The success of a health care intervention is often measured by its impact on the patient’s quality of life. This provides a tool for comparing the success of different treatments, regardless of the condition they are targeting (Swan et al., 2012). Standardised measures of health-related quality of life are used to provide a health utility score. This can then be used to calculate any gains in quality adjusted life years and assess a treatment’s cost effectiveness (Foteff et al., 2016; Saunders et al., 2016). Three generic preference-based questionnaires are commonly used to provide a measure of health utility; EuroQol 5 dimensions (EQ-5D), Health Utility Index 3 (HUI3) and Short-form 6 dimensions (SF-6D) (Herdman et al., 2011, Feeny et al., 2002, Brazier et al., 2002). Of these, only the HUI3 is sensitive to changes in hearing and is recommended as the questionnaire of choice for studies evaluating hearing treatments (Summerfield et al., 2019; Arnoldner et al., 2014; Yang et al., 2013).
The HUI3 consists of 15 questions addressing eight individual health attributes: vision, hearing, speech, ambulation, dexterity, emotion, cognition and pain. Each health attribute has 5 or 6 levels and a weighted health utility score assigned to each level which varies by attribute. These scores are then combined to give a measure of the overall health utility (Feeny et al., 2002). Scores range from zero (dead) to one (perfect health) or even a negative score indicating a state worse than dead. HUI3 scores of less than 0.7 are considered to indicate a severe disability, between 0.7 and 0.88 a moderate disability, and 0.89 or better a mild or no disability (Feng et al., 2009). An increase in score of at least 0.03 is thought to represent a noticeable improvement in quality of life for a patient (Feeney et al. 1995) and an increase of 0.1, a minimum clinically important change (UK Cochlear Implant Study Group, 2004). In studies looking at the benefits of fitting acoustic hearing aids, gains in health utility ranged from 0.06 (Barton et al., 2004) to 0.12 (Grutters et al., 2007; Swan et al., 2012). However, scores remain in the moderate to severe disability category even after treatment (Yan et al., 2009). Cochlear implantation (CI) provides an alternative treatment for those with severe to profound hearing loss with overall greater gains in HUI3 scores of ~0.20 (range 0.05 to 0.4, Crowson et al., 2017).
In South Africa approximately 83 % of the population depends on public health and 17% on the private health care market financed by the medical industry. Funding is provided for CIs on an ad hoc basis from the public health sector through Tygerberg Hospital, with large waiting lists for adult candidates. In countries where access to CI is limited, establishing who will benefit most is one way of prioritising treatment. For cochlear implantation, however, outcomes are difficult to predict from preoperative measures (Lazard et al., 2012). An actuarial approach acknowledges this variability in outcomes and expresses the a priori odds of getting a better result post treatment (UK CI study group, 2004). Up until now the definition of a ‘better result’ has been a greater improvement in speech perception outcomes. Improvements in quality of life, however, have consistently been shown to be independent of audiological performance (Crowson et al., 2017), and therefore may be more meaningful for patients.
Few studies have looked at whether the change in HUI3 scores resulting from implantation can be predicted using preoperative factors. The aim of this study was to determine which baseline factors may significantly influence clinically important gains in HUI3. We considered a gain of ≥0.1 in HUI3 multi-attribute score as clinically important based on the literature (UK CI study group, 2004). The intention was to provide a guide for clinicians when counselling potential patients about the benefits of a CI and to help them prioritize candidates in clinics with large waiting lists and limited resources.