Measuring health-related quality of life (HRQOL) is increasingly used to quantify the effect of a health condition on an individual’s life, and to assess the impact of health care interventions. Economic evaluations measure HRQOL in terms of utility, which can be subsequently incorporated along with changes in life expectancy in the calculation of Quality-Adjusted Life Years (QALYs) to compare health outcomes across health interventions in different diseases and disabilities to inform resource allocation. Utility scales usually range from 0 to 1, where full health is assumed to have the value 1 and death the value 0. Some HRQOL measures such as the Health Utilities Index Mark 2 (HUI2), and Mark 3 (HUI3), and EuroQoL Descriptive System (EQ-5D) allow negative scores that express health states considered worse than death.
There are difficulties and limitations in assessing HRQOL in young children. Firstly, children’s growth and development changes rapidly, which may affect the baseline measure of particular health dimensions such as self-care, usual activity or communication ability [1
]. At present, there are no standard instruments for measuring health status in this population. While the HUIs and EQ-5D, generic health status instruments are recognised as valid and reliable for eliciting health status in adults and children aged over four years (for the HUIs and through proxy-assessment) or 14 years (for the EQ-5D) [3
], and are widely used in cost-utility analysis (CUA) [1
], their application for younger age-groups is still controversial [1
]. Furthermore, HRQOL obtained using different instruments can differ substantially even when measured in the same person [9
] a phenomenon that is particularly evident in young children. While some variation in HRQOL scores obtained from different instruments is inevitable, these can be tested in target populations in order to explore the extent of variation between them. Instruments that provide widely differing outcomes might then be considered less appropriate for use in these populations.
A second challenge to the use of HRQOL instruments with young children, is that these should ideally be completed by the target population, posing substantial challenges in very young responders. A review found that only 2% of studies where children were the primary beneficiaries of the intervention estimated HRQOL scores directly from this age-group [1
]. This is expected given the greater difficulties children might face in accurately describing their health condition during and after illness episodes. In addition, some of the questions might be too complex for young children to answer. As a result, proxy-assessment, where children’s health status is obtained through their caregivers, physicians, or adult patients with similar health conditions, is applied [11
]. However, self- and proxy-assessed HRQOL scores may vary, even when using the same tools [12
Based on this review, two potential sources of variation are present when assessing HRQOL in young children: 1) variation due to the choice of instrument; 2) variation between the measures obtained from patients directly as opposed to their carers. The agreement between self-reported and proxy measures of health status in ill children is not well established and there are no clear guidelines as to whether this is acceptable practice [12
]. Where the use of a proxy is not appropriate, better guidance is needed on the most appropriate tools for health status measurement in young children.
This study explores the use of instruments for HRQOL measurement in young children affected by infectious diseases in Thailand, and is a part of a CUA of 10- and 13-valent pneumococcal conjugate vaccines. Assessment using various HRQOL instruments by the caregivers and affected children (who are able to rate their health status) can provide the necessary data to address the above knowledge-gap.
The specific objectives of this study are to 1) quantify the variation in scores derived from young patients and their carers using different HRQOL instruments in different health conditions; 2) provide recommendations as to whether it is appropriate to measure HRQOL of paediatric patients using their caregivers’ assessments; 3) where proxy assessment is not appropriate, identify which instrument is most suitable for use in very young children.