The test-retest reliability of the modified patient generated index

Objectives: The purpose of this study was to determine the test-retest reliability of the recently modified Patient Generated Index (PGI) when used as a self-completed postal questionnaire by older people with arthritis. Methods: Two sets of postal questionnaires were used, sent two weeks apart, followed by interviews with a theoretically chosen subsample of respondents to both. Reliability for respondents whose health had not changed in the intervening two weeks was assessed using intraclass correlation coefficients. Data from interviews were used to develop theories to select subgroups for analysis. Results: One thousand one hundred and twenty-nine people over 65 years old with arthritis were surveyed and 53 were selected for interview. The response rates to the two surveys were 78% and 83%, respectively. Complete data for the test-retest analysis were available from 236 (29.2%) respondents. The intraclass correlation coefficient (ri) was 0.55 [95% confidence interval (CI) 0.43 to 0.64, P