Precision in a clinical chemistry laboratory

SYNOPSIS The assessment of accuracy and precision in a routine clinical chemistry laboratory is discussed. A figure and tables are presented which relate the chance of making incorrect clinical decisions to the precision of an analytical method. The question of accuracy and precision in clinical chemistry is frequently discussed (see, for instance, Thompson and Jones, 1965; Mitchell, 1966). It is a waste of time in routine practice to strive for a degree of accuracy or precision which is greater than that required by clinicians. The object of this communica-tion is to enable the performance of a laboratory method to be judged quantitatively in relation to clinical needs. 'Accuracy ' is the extent to which a method measures what it sets out to measure. Determinations by an accurate method will not show systematic error, i.e.