Lower confidence limits for critical systematic errors.
OBJECTIVE
The critical systematic error (DeltaSE(C)) can be used to select a quality control scheme. It is just an estimate of the true DeltaSE(C), however, and its precision depends on the sample size. Thus, the lower confidence limit (LCL) of DeltaSE(C) should be adopted instead to guard against false optimism.


METHODS
LCLs are calculated as a function of DeltaSE(C) and sample size using a modified version of Bissell's formula.


RESULTS
The uncertainty in DeltaSE(C) may be significant. The largest relative difference between DeltaSE(C) and its LCL is 52.2%, for DeltaSE(C)=2 and n=20. This difference decreases with increasing DeltaSE(C) and sample size.


CONCLUSIONS
It is shown that taking into account the uncertainty in DeltaSE(C) can greatly influence quality control planning decisions. Caution should thus be exercised when interpreting control data and choosing an appropriate quality control strategy. The derived equation for LCL is simple, and can be immediately applied to practical solutions.
Gernand
Wojciech
W
Department of Clinical Biochemistry, Jagiellonian University Medical College, ul. Kopernika 15b, 31-501 Krakow, Poland. gernand@wp.pl
Dumnicka
Paulina
P
Kuśnierz-Cabala
Beata
B
Kapusta
Maria
M
Solnica
Bogdan
B
D000704:Analysis of Variance; D002784:Cholesterol / Q000097:blood; D016001:Confidence Intervals; D003627:Data Interpretation, Statistical; D006801:Humans; D008954:Models, Biological; D015233:Models, Statistical; D011786:Quality Control; D018401:Sample Size