| Abstract: | A method is presented for engineering the necessary levels of measurement reliability for evaluating ongoing programs. Two studies of levels of client functioning at a community mental health center (CMHC), in which an outcome measure, the Global Assessment Scale (GAS), did not perform as expected, drew attention to the need for better control of outcome measure reliabilities. Drawing from generalizability theory, a study was conducted of three sources of GAS score variance — clients, raters, and training in the use of the scale. Several estimates of reliability (ERs) were developed, depending on the manner in which the GAS ratings were, or would be, obtained in the CMHC. The differences among these ERs clarified why the GAS had lower reliability when used in our setting. Finally, two hypothetical examples are described to illustrate the utility of applying generalizability theory to achieve higher reliabilities for outcome measures. |
