Patient centered assessment of ankylosing spondylitis-specific health related quality of life: evaluation of the Patient Generated Index

Abstract

Objective: To evaluate the Patient Generated Index (PGI) for the measurement of individualized health related quality of life in ankylosing spondylitis (AS).

Methods: The PGI asks patients to nominate areas of their lives affected by their disease that they consider the most important. Semistructured interviews with AS patients produced a trigger list of areas of life affected by AS. The PGI was self-completed by UK patients taking part in a multicenter postal survey. The instrument was assessed for data quality, reliability, validity, and responsiveness.

Results: The PGI had acceptable completion rates. Scores covered the available range and approximated normality. Test-retest reliability estimates support the use of the PGI in group evaluation (intraclass correlation coefficient > 0.80). Comparisons with scores for other health status instruments provided evidence for the validity of the PGI. The largest levels of correlation were found for the AS Quality of Life Questionnaire (ASQoL) and the EuroQol. The informed and open format of the PGI had the strongest linear relationship with responses to both specific and general health transition questions (p < 0.01), and was the most responsive format of the PGI.

Conclusion: The PGI is the first AS-specific individualized measure of health related quality of life. There is good support for the content validity of the instrument and patient acceptability is high. Adequate levels of data quality and reliability support the use of the PGI in group evaluation. Moderate levels of responsiveness to changes in health were produced by the informed and open format of the PGI.