Example of Operating Characteristic Curves

Use the OC Curve platform to estimate the probability of identifying a process shift with the first sample collected after the shift.

1. Select Analyze > Quality and Process > OC Curves.

2. Select XBar Shewhart Chart.

3. Click OK.

4. Set the control limits to -1.34 and 1.34. These are 3 sigma limits for s = 1 and n = 5 (3 times 1 divided by the square root of 5).

5. Leave Sigma set to 1 and the sample size at 5.

6. Set Shift to 2.

Figure 18.1 OC Curve Example 

The Y axis is the Beta risk, or the probability of not detecting a shift. The probability of detecting a shift of size 2s with a sample of size 5 is 1 - 0.07 = 0.93.

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