CREATION AND VERIFICATION OF REFERENCE INTERVALS

Reference intervals remain the most common means of determining whethe r an observed value suggests the presence of disease. When creating re ference intervals, one must look at the requirements for the preanalyt ic, analytic, and postanalytic phases. For the preanalytic phase, inve stigators use exclusion and partition criteria to create the sample po pulation. During the analytic phase, the investigator should use contr ol charts to ensure that the system is in good control. During the pos tanalytic phase, the investigator uses the nonparametric approach, whi ch involves establishing the 2.5 and 97.5 percentiles reference limits . This is the fourth and final article in a continuing education serie s on statistics. Other articles in this series dealt with control char ts, the use of linear regression to compare methods, and linearity ass essment in the laboratory. The exam follows this article.