Health status assessment for the twenty-first century: item response theory, item banking and computer adaptive testing.

Health status assessment is frequently used to evaluate the combined impact of human immunodeficiency virus (HIV) disease and its treatment on functioning and well-being from the patient's perspective. No single health status measure can efficiently cover the range of problems in functioning and well-being experienced across HIV disease stages. Item response theory (IRT), item banking and computer adaptive testing (CAT) provide a solution to measuring health-related quality of life (HRQoL) across different stages of HIV disease. IRT allows us to examine the response characteristics of individual items and the relationship between responses to individual items and the responses to each other item in a domain. With information on the response characteristics of a large number of items covering a HRQoL domain (e.g. physical function, and psychological well-being), and information on the interrelationships between all pairs of these items and the total scale, we can construct more efficient scales. Item banks consist of large sets of questions representing various levels of a HRQoL domain that can be used to develop brief, efficient scales for measuring the domain. CAT is the application of IRT and item banks to the tailored assessment of HRQoL domains specific to individual patients. Given the results of IRT analyses and computer-assisted test administration, more efficient and brief scales can be used to measure multiple domains of HRQoL for clinical trials and longitudinal observational studies.