OBJECTIVE: To compare three separate methods for establishing interpretability 
for a health status measure, the Hydrocephalus Outcome Questionnaire (HOQ).
STUDY DESIGN AND SETTING: The mothers of children with hydrocephalus attending 
the outpatient clinics at a pediatric hospital completed the HOQ (for which 
scores can range from 0 to 1.0 with the smallest possible incremental change 
being .005), the Health Utilities Index-2 (HUI-2), and a global rating of their 
child's health. The surgeon for the child also provided a global rating of the 
child's health following their visit. These data were used to calculate (i) the 
minimal important difference (MID) based on global health ratings, (ii) the MID 
based on an effect size approach, and (iii) the conversion of numerical HOQ 
scores into health utility scores obtained from the HUI-2.
RESULTS: Based on mothers' responses (n = 79) and surgeons' responses (n = 61), 
respectively, the MID for the HOQ was estimated to be .12 and .10. Using the 
effect size approach, the MID was estimated to be much lower at .03. HOQ scores 
were found to be readily translatable to HUI-2 utility scores using a simple 
linear transformation. The mean utility score for this sample of patients was 
.77.
CONCLUSIONS: Two methods for determining the MID yielded quantitatively 
different results. Conversion of numerical health status scores to utility 
scores was done successfully and providing another element of interpretability.