Interval estimation for statistical control
In order to develop meaningful statistical control limits when applicable based upon the normal distribution, the mean and the standard deviation of a population must be known. In cases when an accurate approximation of the standard deviation is not known, the calculation of reasonable statistical control limits can be performed by using the Student's tdistribution. The Student's tvalue for n1 degrees of freedom (n is the sample size) and the confidence intervals that correspond to 20 and 30 (95.45% and 99.73% respectively) is used to determine control limits from a relatively small data set. The control limits with this method are obtained by multiplying the calculated standard deviation of the data set by the appropriate tvalue for the specified confidence level and degrees of freedom While the tdistribution method is needed primarily for a small sample size (n <30), it approaches the normal distribution with increasing n, and hence can be used for any size sample.
Year of publication: 
20080205


Authors:  ABDURRAHAM, N.M. 
Subject:  general and miscellaneous//mathematics, computing, and information science  DEGREES OF FREEDOM  DATA COVARIANCES  CALCULATION METHODS 
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