Minimum skills required by children to complete health-related quality of life instruments for asthma: comparison of measurement properties

To gain a complete picture of a child's health-status, measurement of health-related quality of life (HRQL) is necessary. Since parents do not accurately perceive children's HRQL, information must be obtained from the children themselves. The aim of this study was to determine the minimum age and reading skills required by children to complete competently the Paediatric Asthma Quality of Life Questionnaire (PAQLQ), the Health Utilities Index (HUI), the Feeling Thermometer and the Standard Gamble, and to evaluate the validity of each for measuring HRQL in children with asthma. Fifty two children (age 7-17 yrs) with symptomatic asthma participated in a 9 week single cohort study with HRQL and clinical asthma control assessed every 4 weeks. All children provided very reliable data for the PAQLQ and the HUI but they needed > or = grade 6 reading skills to complete the Standard Gamble and > or = grade 2 skills for the Feeling Thermometer. In those children who were able to provide reliable data, the PAQLQ had the best discriminative and evaluative measurement properties, followed closely by the Feeling Thermometer. Measurement properties in the Standard Gamble were weaker and although the HUI was very reliable it was not actually measuring asthma-specific HRQL. The Paediatric Asthma Quality of Life Questionnaire may be used with confidence in clinical studies and practice to provide a profile of children's day-to-day experiences. In those children with adequate skills to complete the test reliably, the Feeling Thermometer provides a good estimate of the value that children place on their asthma health status.