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Confidence Interval

Suppose that sample of items is taken at random from a process and the mean of the  sample is used as an estimator of the process mean. This sample mean is a point estimate, and is unlikely to exactly equal the true population mean.

The confidence interval defines a band around the sample mean within which the true population will lie, to some degree of confidence: For example, there is a 95% probability that the true population mean will lie within the 95% confidence interval of the sample mean. The method used to calculate the confidence interval will vary, but usually involves the normal distribution for large samples, or the t-distribution for small samples.

The 100(1-α )% confidence interval for the mean of a small sample (t distribution) is:  Analytical and descriptive statistics are covered in the MiC Quality online course Primer in Statistics. Try out our courses by taking the first module of the Primer in Statistics free of charge. :: Six Sigma Primer :: Primer in Statistics :: Advanced Statistics :: Statistical Process Control SPC :: Advanced SPC :: Design of Experiments :: Advanced DOE :: Measurement Systems Analysis MSA/ Gage R&R Primer in Statistics FREE First Module "Introduction to Statistics" Primer in Statistics FREE Reference Booklet FREE Excel Primer 