Acceptance Sampling by Attributes
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Stat > Quality Tools > Acceptance Sampling by Attributes

Allows you to create an attribute acceptance sampling plan or compare various sampling plans that you specify.

·    Create a sampling plan to determine a sample size and make a decision whether to accept or reject an entire lot (batch) of product, based on the number of defectives or defects found in that sample.

·    Compare multiple sampling plans to determine the effects of varying sample size or acceptance number.

Dialog box items

Create a sampling plan: Choose to determine a sample size and the criteria for accepting or rejecting an entire lot.  

Compare user defined sampling plans: Choose to see how effective your current sampling plan is and to compare various competing plans.  

Measurement type: Choose Go/no go (defectives) if you inspect units and record whether the product is defective or not. Choose Number of defects if you inspect units and count and record the number of defects per unit.

Units for quality levels: Choose the units based on your measurement type.

If you specified Go/no go (defectives), then choose either Percent defective (0-100), Proportion defective (0-1), or Defectives per million to represent the level of defectives in the process.

If you specified Number of defects, then choose either Defects per unit, Defects per hundred, or Defects per million to represent the level of defects in your process.

Acceptable quality level (AQL): Enter a number to represent the largest number of defectives or defects in a process that will still be considered acceptable. Typically, a sampling plan is designed to give a high probability of acceptance at the AQL.
You must specify the AQL when you create a sampling plan, but it is not required for comparing sampling plans. The AQL must be consistent with measurement units. For example, with percent defectives 0<AQL<100; with proportion defective 0<AQL<1; and with defectives per million 0<AQL<1,000,000.

Rejectable quality level (RQL or LTPD): Enter a number to represent the number of defectives or defects in an individual lot that you are willing to tolerate. Typically, a sampling plan is designed to give a low probability of acceptance at the RQL.
You must specify the RQL when you create a sampling plan, but it is not required for comparing sampling plans. The RQL must be entered consistently with measurement units and must be larger than the AQL. For example, with percent defectives AQL<RQL<100; with proportion defective AQL<RQL<1; and with defectives per million AQL<RQL<1,000,000.

Lot size: Enter a number to represent the lot size or batch size of the entire shipment that you will accept or reject based on sampling results. You don't need to specify a lot size if you specify the AQL, RQL, and alpha and beta risks; however, Minitab requires the lot size to calculate the AOQ curve and the ATI curve.

For Creating Sampling Plans

Producer's risk (Alpha): Enter a value between 0 and 1 to represent a. 1- a represents the desired probability of accepting a lot at the AQL, which is necessary for creating the sampling plan.

Consumer's risk (Beta): Enter a value between 0 and 1- a to represent b. b represents the desired probability of accepting a lot at the RQL, which is necessary for creating the sampling plan.

For Comparing User Defined Sampling Plans

Sample sizes: Enter positive integers to specify the sample sizes you wish to compare.

Acceptance numbers: Enter positive values to specify the acceptance numbers you wish to compare.

Use these guidelines to enter sample sizes and acceptance numbers:

·    Specify one sample size and several acceptance numbers to look at the effect of just varying acceptance number.

·    Specify multiple sample sizes with just one acceptance number to look at the effect of just varying sample size.  

·    Specify combinations of sample size and acceptance number to look at specific paired combinations. Use the same number of sample sizes and acceptance numbers.

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