Variables Sampling Plans Based on the Normal Distribution

Sampling Plans are considered which call for the acceptance of a lot of material if both – ks ≥ L and + ks ≤ U, where L and U are the lower and upper specification limits and where and s are the sample mean and standard deviation and k is an appropriate constant. Some errors that need to be corrected in previous work are pointed out in interpretation of the mathematical formulas before plans of the type described can be properly applied. Tables are given for the constant k under two different circumstances. Table II applies when the sum of the proportions defective in the two tails of a normal distribution is to be controlled. Table III applies when each tail is to be controlled below preassigned values, i.e., so that one can say with probability y that the proportion in the lower tail (below L) of accepted lots does not exceed a preassigned value and simultaneously the proportion in the upper tail (above U) does not exceed its preassigned value. The same constants, in Table III, apply when all the defect...