Qualitative Evaluation of a Test's Bias and Imprecision

Laboratories can access information about imprecision using interlaboratory comparison reports supplied by the vendor of their control materials. While these reports can also be used to evaluate bias, some laboratories prefer proficiency report data for this purpose.

Participants in the Bio-Rad Unity™ Interlaboratory Program can use the Laboratory Comparison Report, the Laboratory Performance Overview Report, or the Statistical Profile Report. These reports contain two relevant statistics for qualitative assessment of laboratory bias and imprecision:

• CVR (coefficient of variation ratio)

  CVR is a peer-based evaluation of imprecision. The ratio is calculated as the laboratory coefficient of variation (CV) for the test divided by the average CV reported for the consensus group.

• SDI (standard deviation index)

  SDI is a relative peer-based estimate of bias.

SDI describes or quantifies bias (the difference between the laboratory's observed mean and the consensus group mean) in terms of standard deviation.

OPSpecs Charts and sigma values are available in the optional Westgard Advisor™ online and provide information about a test's maximum allowable bias (inaccuracy) and imprecision. See "Westgard Advisor™ online" for more information.