Measurement precision test construction and best test design

This article examines the precision of measurements obtained from using the Rasch Dichotomous Model to analyse test data. Considering tests in which the item difficulties are uniformly spaced from easiest to most difficult, permits the derivation of an alternative expression for the standard error of measurement. This expression is sufficiently simple to enable the precision properties of uniform tests to be readily described and to enable a variety of problems of test construction to be solved. One particular problem is that of best test design. Regarding measurement precision as a property of the test only, we show that the best uniform test of a given length and a given target interval is the one that satisfies a minimax condition on the standard error. We illustrate the solution to this problem and describe properties of best tests

Performance status assessment in home hospice patients using a modified form of the Karnofsky Performance Status scale

The Karnofsky Performance Status (KPS) scale is considered to be the gold standard for quantifying the physical functioning of patients with cancer. However, problems have been identiffed with the scoring system when the scale is used in the home hospice setting. The goal of this study was to compare assessments of performance status using two instruments, the KPS and a modified version, the Thorne-KPS (TKPS). The TKPS avoids reference to location of care and has new descriptors for assessing the frequency of professional visits and the proportion of time spent in bed. Comparisons were made on a sample of 78 home-hospice patients in Perth, Western Australia. The median score for both scales was 60. The scales agreed in 56% of ratings overall but after correcting for chance, agreement was reduced to 47%. However, 91% of the 34 discrepancies occurred within one or two levels of the 11-point scale. TKPS scores were consistently lower than KPS scores and were spread over a wider range of the scale. The strongest agreement occurred at the higher levels of performance and the weakest agreement was within the middle levels of the scales. Further studies are required to determine which of the two scales more accurately reflects performance status and survival time. However, the results to date suggest that the TKPS may be a more objective and sensitive measure of functional performance in home hospice patients