Acceptable Standard Deviation (SD)

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The page below is a sample from the LabCE course Quality Control. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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Acceptable Standard Deviation (SD)

  • A small SD represents data where the results are very close in value to the mean. The larger the SD the more variance in the results.
  • Data points in a normal distribution are more likely to fall closer to the mean. In fact, 68% of all data points will be within ±1SD from the mean, 95% of all data points will be within + 2SD from the mean, and 99% of all data points will be within ±3SD.
  • Statisticians have determined that values no greater than plus or minus 2 SD represent measurements that are closer to the true value than those that fall in the area greater than ± 2SD. Thus, most QC programs require that corrective action be initiated for data points routinely outside of the ±2SD range.