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GCSE Statistics · key term
A boundary beyond which a sample result needs checking by taking another sample immediately. For sample means, warning limits are set at two standard deviations of the sample means above and below the expected value.
Used by Edexcel
Specification 2g.02 · Paper 1, Paper 2
Revise: Action and warning linesWhen the process is working correctly, about 95% of sample summary values fall inside the warning limits. This means about 1 in 20 falls outside them through ordinary random variation. A warning therefore suggests a possible problem; it does not prove that the machinery is faulty.
About 1 in 20 outside the warning limits refers to both tails combined, not 1 in 20 on each side.
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