How does the EQ-5D-Y Proxy version 1 perform in 3, 4 and 5-year-old children?

Background The EQ-5D-Y Proxy is currently recommended for Health Related Quality of Life (HRQoL) measurement in children aged 4-8 years of age. However, it has only been validated in children over six years of age. The aim of this study was to investigate the performance of the EQ-5D-Y proxy version 1 in children between the ages of 3-6 years. Methods A sample of 328 children between 3 and 6 years of age were recruited which included children who were either acutely-ill (AI), chronically-ill (CI) or from the general school going population (GP). The EQ-5D-Y Proxy Version 1 and the PedsQL questionnaires were administered at baseline. The EQ-5D-Y Proxy was administered telephonically 24 h later to children with chronic illnesses to establish test-retest reliability. The distribution of dimensions and summary scores, Cohen's kappa, the intraclass correlation coefficient, Pearson's correlation and Analysis of variance were used to explore the reliability, and validity of the EQ-5D-Y for each age group. A single index score was estimated using Latent scores and Adult EQ-5D-3 L values (Dolan). Results The groups included 3-year olds (n = 105), 4-year olds (n = 98) and 5-years olds (n = 118). The dimension Looking after Myself had the greatest variability between age groups and had the highest rate of problems reported. Worried, Sad or Unhappy and Pain or Discomfort were not stable across time in test-retest analysis. The Visual Analogue Scale (VAS), and single index scores estimated using the latent values and Dolan tariff had good test retest (except for the latent value scores in a small number of 4-year olds). EQ-5D-Y scores for all ages had small to moderate correlations with PedsQL total score. The EQ-5D-Y discriminated well between children with a health condition and the general population for all age groups. Caregivers reported difficulty completing the Looking after Myself dimension due to age-related difficulties with washing and dressing. Conclusion The dimension of Looking after Myself is problematic for these young children but most notably so in the 3 year old group. If one considers the summary scores of the EQ-5D-Y Proxy version 1 it appears to work well. Known group validity was demonstrated. Concurrent validity was demonstrated on a composite level but not for individual dimensions of Usual Activities or Worried, Sad or Unhappy.. The observable dimensions demonstrated stability over time, with the inferred dimensions (Pain or Discomfort and Worried, Sad or Unhappy) less so, which is to be expected. Further work is needed in exploring either the adaptation of the dimensions in the younger age groups.