# Calculating Acceptable Ranges

**How to Subscribe**

MLS & MLT Comprehensive CE Package Includes 154 CE courses, most popular | $95 | Add to cart |

Pick Your Courses Up to 8 CE hours | $50 | Add to cart |

Individual course | $20 | Add to cart |

Need multiple seats for your university or lab? Get a quote

The page below is a sample from the LabCE course

Learn more about Introduction to Quality Control (online CE course)

**Introduction to Quality Control**. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.Learn more about Introduction to Quality Control (online CE course)

Calculating Acceptable Ranges

Many physical and biological processes are well-modeled by a distribution having a roughly bell-like shape. This curve is called the gaussian, bell curve, or normal distribution. The normal distribution has the following characteristics:

- 68.3% of the area lies between the mean minus one standard deviation (1 SD) and x¯ plus 1 SD;
- 95.5% of the area lies between x¯ - 2 SD and x¯ + 2 SD; and
- 99.7% of the area lies between x¯ - 3 SD and x¯ + 3 SD.

For example, if a certain control gives a mean test result of 5.6 with an SD of 0.8, then 95.5% of future control test values will be in the range of 4.0 - 7.2, which is two standard deviations of the mean. Values that fall outside of these limits may not be acceptable (depending on the laboratory's QC rules) and could indicate a problem with the measuring system.