Objectives: To develop a Computerized Adaptive Test to obtain a generic measure of the patients' perceived health state.
Methods: An experts' panel created a pool of five-alternative Likert format items, chosen among Health Related Quality of Life questionnaires validated in our country. That pool was applied to a pilot sample and later to another general sample of patients belonging to 7 Primary Health Centers in Asturias. Two response options were offered to the general sample: 1) on paper 2) on a touch panel. The Item Response Theory psychometric properties (discrimination, reliability and validity) were evaluated by means of the factorial analysis and other methods. The information function was analyzed and a study of simulation was developed.
Results: A pool of 140 items was created. The requirements for the application of the IRT were verified by means of the factorial analysis. A selection of items was realized following the statistical criterion and the application of the IRT. The elimination of 35 articles resulted in a test composed by 105 items. Once the questionnaire was applied to the general sample, the parameters of the items were estimated again. The parameters invariance was verified once more and other 9 items were eliminated. The result was a definitive version of 96 items.
Conclusions: The Computerized Adaptive Test developed proves to be a fast and reliable tool to evaluate the Health Related Quality of Life generically. This test may imply a very important advance for the measurement of the results reported by the patients in the clinical practice.