Quick Review Cards for Medical Laboratory Science

Quality Control Statisticscontinued

TERM EXPLANATION

Normal distribution The Gaussian bell-shaped curve:

68% of values fall within ±1 SD of mean

95% of values fall within ±2 SD of mean (95% confidence interval)

99.7% of values fall within ±3 SD of mean

68%

95%

–2s –1s X +1s +2s

Gaussian frequency distribution with
95% limits indicated. (From Arneson W,
Brickell J. Clinical Chemistry: A Laboratory
Perspective. Philadelphia: FA Davis; 2007:54.)

Laboratory Operations Review 49