Alternative statistical approach to evaluating interlaboratory performance.

We report a new technique for realistic assessment of laboratory performance as measured by proficiency testing. Interlaboratory results accumulated from 129 participants during 18 months provide the baseline data from which we established "state-of-the-art" performance criteria for three ranges of pH, pCO2, and pO2. By concurrent use of two statistical measurement techniques, the cumulative percentile rank and the algebraic and absolute mean error, laboratories can accurately evaluate their performance in terms of acceptable state-of-the-art criteria, total error, or medical usefulness. The approach facilitates assessment of the nature of the errors that have led to inferior performance and identification of probable areas where improvement is possible. If criteria based on regulatory standards or medical usefulness goals are included, the system can provide a basis for licensure or professional quality improvement.