Process Analysis Sampling Plans - Fixed Sampling Plans
To construct a simple sampling plan, we would first decide on a sample size, based on the means under H0/H1 and the particular Alpha and Beta error probabilities. Then, we would take a single sample of this fixed size and, based on the mean in this sample, decide whether to accept or reject the batch. This procedure is referred to as a fixed sampling plan. Process Analysis allows you to "play around" with the different parameters that determine the sample sizes, or to enter a sample size and to estimate the resultant Beta error probability.
- Operating characteristic (OC) curve
- The power of the fixed sampling plan can be summarized via the operating characteristic curve. In that plot, the probability of rejecting H0 (and accepting H1) is plotted on the y-axis, as a function of an actual shift from the target (nominal) specification to the respective values shown on the x-axis of the plot. This probability is, of course, one minus the Beta error probability of erroneously rejecting H1 and accepting H0; this value is referred to as the power of the fixed sampling plan to detect deviations. Also indicated in this plot are the power functions for smaller sample sizes.
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