The Percentage of Client Improvement visual provides information on the percentage of clients who show change over time on the ACORN questionnaires. Change is classified as "significant" if the change is greater than the Reliability Change Index (RCI). If the change is greater than the Standard Error of Measurement (SEM), the change is classified as "somewhat improved/worse". Change that does not exceed the Standard Error of Measurement is classified as "No Change".
The probability of change is in part a function of the intake score...scores at the extremes of the distribution will tend to change more than scores near the middle. This means that simple classification of % of patients improved that is based on raw score change can be misleading, as the results are dependent on the case mix. For this reason, we calculate the % of patients that change based on the Severity Adjusted Effect Size (SAES), which controls for differences in case mix.
The SEM and RCI are dependent on the reliability of the measure. The reliability will vary depending on the number of items in the magnitude of correlation between items. For ACORN questionnaires, the average reliability is very close to .9. Using this estimate of reliability, the Reliable Change Index is the equivalent of .8 effect size, while the standard error of measurement averages .3 effect size. In order to assure that all variations of the questionnaires produce a comparable distribution of change, the cut scores of .3 and .,8 effect size are used consistently on all questionnaires.