Improved Detection of Serum Estradiol after Sample

application of the cross-run rules. Data were also modeled for n 4, and the error detection for full multirules was lower than described on the Westgard site for all changes in bias from 1.0 to 3.0 times the SD when previously detected shifts were removed from the 8x rule (data not shown). The change in bias that can be detected with 90% certainty decreases from 1.8 times the SD, as shown on the Westgard website, to 2.5 times the SD, the same change in bias that can be detected with the use of within-run rules only. The above data suggest that the true power of error detection of cross-run rules is markedly less than has previously been claimed. It can be seen that the action of the cross-run rules conforms with previous descriptions as warning rules for detecting smaller shifts in assay bias than are easily detectable by common within-run rules. However, these rules cannot detect these minor shifts with any certainty. For example, the 41s rule will detect assay changes a maximum of 25% of the occasions an otherwise unidentified change occurs. However, the present study was limited to evaluation of changes in bias at a single point in time. It is likely that cross-run rules may be more useful in detecting a gradual change in bias over time because such changes may be less likely to be detected previously by within-run rules. It is important that laboratory scientists be aware of the performance characteristics of the QC protocols in use in their laboratories. Reliance on within-run rules is preferable to rules requiring data from multiple runs because errors can be detected sooner after they have occurred. However, if cross-run rules are to be used they are of value only if they add to the error detection generated by the rules that have already evaluated the data that are required for them to fire. By excluding previously detected changes in assay bias, I have demonstrated that the cross-run rules 10x and 41s with n 2 and 8x with n 4 have a lower probability of error detection than is shown in the data on the Westgard website and do not add to error detection at the 90% confidence level derived by use of within-run rules.