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In This Section |
A type of systematic error evidenced by an abrupt change in the mean of the control values.
The standard deviation measures a test's precision, or how close individual measurements are to each other. (The standard deviation does not measure bias, which requires comparing results to a target value such as the Peer consensus group.) The standard deviation provides an estimate of how repeatable a test is at specific concentrations. Test repeatability can be consistent (low standard deviation, low imprecision) or inconsistent (high standard deviation, high imprecision). Use the following formula to calculate the SD:
The standard deviation index is a measurement of bias (how close a value is to the target value). The Unity™ Interlaboratory Program uses the consensus group value as the target value. Use the following formula to calculate the SDI:
A set of rules which use statistics to monitor and evaluate a process. SPC rules include the original six Westgard rules as well as additional rules.
Note: The Statistical Profile Report is optional. Contact your Bio‑Rad QC Program Representative to request this report.
The Statistical Profile Report allows you to compare your laboratory's statistics to the Peer, Method, and All Labs consensus group statistics for selected time periods. The Statistical Profile Report also provides two histograms summarizing how your laboratory's mean and CV compare to the range of mean and range of CVs calculated for each consensus group.
The mean, SD, and number of points for a data set comprised of the control material results for testing an analyte over a specific time range (for example, October 2007).
Data points violating any SPC rule set to reject or warn.
A trend or shift away from the laboratory mean. Small amounts of systematic error are tolerable. Systematic error remains until corrective action is taken.