Ingrained for many years in the science of educational assessment were a large number of "truths" about how to make sense out of testing results, artful wisdoms that appear to have held away largely by force of habit alone. Practitioners and researchers only occasionally agreed about how tests should be designed, and were even further apart when they came to interpreting test responses by any means other than categorically "right" or "wrong." Even the best innovations were painfully slow to be incorporated into practice. The traditional approach to testing was developed to accomplish only two...