Total Error (TE) and Total Allowable Error (TEa)

Total error and total allowable error are useful when choosing the SPC rule(s) to apply to a test. For example, SPC rules can identify a test exceeding a quality specification (TE_a). Total error for a test includes both bias and imprecision at a 99% confidence interval. Use the following formula to calculate the TE:

TE_a specifications are available from several sources as described in "Determine Quality Requirements for the Test." After choosing a TE_a, calculate the TE budget. Use the following formula to calculate the TE budget:

With the optional Westgard Advisor™ online, choose a TEa and the program suggests SPC rules based on test data and Unity™ Interlaboratory Program information.