Sample Size Determination for Lower Confidence Limits for Estimating Cpk

摘要

Until recently, estimates of process capability indices have been point estimates. However, a more appropriate estimate would be provided by a confidence interval. In this case, a one-sided interval is necessary, since the real interest is in how small the process capability index can be. This paper provides two equations to estimate the sample size necessary to achieve a desired one-sided lower confidence limit with specified confidence level, makes a comparative study between the two equations. The conservative sample size should be 30 and the optimal 50-100.