Interpret the key results for Variables Acceptance Sampling (Accept/Reject Lot)

After you create a variables acceptance sampling plan to determine the sample size and acceptance criteria for each incoming lot, you can analyze the measurement data from a sample to determine whether to accept or reject an entire lot of a product. Collect a sample, according to the plan sample size, and record the measurements of a single measured characteristic, such as thickness, concentration, or surface roughness. Minitab uses your data from particular lots and the information from the sampling plan to determine the lot decision.

For variables sampling plans, you can examine only one measurement per sampling plan. For example, if you need to inspect for wafer thickness and wafer width, you need two separate sampling plans.

The manufacturer will accept the lot if it meets the following three conditions:
  • Standard deviation is less than the maximum standard deviation.
  • Z.LSL is greater than or equal to the critical distance.
  • Z.USL is greater than or equal to the critical distance.

Acceptance Sampling by Variables - Accept/Reject Lot

Make Accept or Reject Decision Using Thickness Sample Size 259 Mean 0.403108 Standard Deviation 0.0469204 Lower Specification Limit (LSL) 0.395 Upper Specification Limit (USL) 0.415 Z.LSL 0.172803 Z.USL 0.253452 Critical Distance (k Value) 3.44914 Maximum Standard Deviation (MSD) 0.0027533 Decision: Reject lot.
Key Results: Z.LSL, Z.USL, Critical Distance, Maximum Standard Deviation, Decision

In these results, the standard deviation is 0.0469204, which is greater than the maximum standard deviation of 0.0027533. The Z.LSL and Z.USL values are less than the critical distance of 3.44914. The manufacturer rejects the lot.

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