Abstract: An improved procedure for statistically evaluating the performance, precision and/or accuracy, of at least one analytical instrument in a pool of like or substantially like instruments by comparing the performance of the one instrument located in one laboratory with the performance of like instruments in other laboratories. The procedure includes the step of quantitatively analyzing a reference or control specimen of known constituents by each instrument in the pool and collecting the resultant data from the one instrument in the pool and of the pool instruments. The mean data from the one instrument and of the pool instruments are mathematically correlated in a series of statistical equations for computing a novel, sensitive index known as the "Instrument Performance Index" or IPI.