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.