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Confidence Limits on a Percent Defective Characterized by Two Specification Limits

Summary: A quality problem is to assess the performance of a production process with respect to specifications. A solution is obtained by estimating the percent defective and placing confidence limits on the percent defective for each product characteristic. Tables are presented in this paper for determining a point estimate of the percent defective and 90, 95, and 99 percent confidence limits on the percent defective of a characteristic with both upper and lower or single specification limits. On the assumption of normality, only the specification limits, sample size, sample mean and standard deviation are needed to give a solution to the problem.

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  • Topics: Statistics
  • Keywords: Confidence intervals, Defects, Specification limits
  • Author: Kirkpatrick, R.L.
  • Journal: Journal of Quality Technology