Principles of Quality Assessment
Quality assessment techniques consist of ways in which the measurement process may be monitored in order to infer the quality of the data output. They provide assurance that statistical control has been achieved and is maintained as well as estimates of the accuracy of the data. The quality assessment techniques are classified as internal or external according to the source of the assistance needed to implement the assessment technique. Internal test samples may consist of internal reference materials, split samples, spiked samples, and surrogates which are measured in suitable test routines to evaluate the precision of the measurement process. External evidence for the quality of the measurement process is important for several reasons. First, it is the easiest approach in that it can minimize much of the effort required for internal evaluation. Second, it minimizes the danger of error due to introspection.