Sampling
The quantity of products to be inspected is called the "Sample Size". It can be so many per hour, batch or %. e.g. 20 per hour, 20 per 1000 or 5%.
Too big a sample would be uneconomical. Inspection costs the company, inspection is a loss of profit. Too small a simple would not find out how many products were faulty. The sample size could be different at different Critical Control Points.
Sampling.
A quantity of products are taken from a batch and inspected to establish if the products reach acceptable quality standards or not.
| Sample Size | Number of products in the sample. |
| Single sampling | Inspection of a single sample decides if sample is acceptable. |
| Double sampling | Inspection of a sample leads to acceptance, rejection or leads to a second sample being taken. This sample is either accepted or rejected. |
Sampling Level
Calculating the relationship between "Batch Size and "Sample Size" takes complex calculations.
Inspection levels determine the relationship between Batch and Sample size. Levels I II & III are general inspection levels used by the US. Military, ISO 2859 is used in Europe.
| II | Normal level. |
| I | Half the Normal level. Used where recent quality history has been excellent. |
| III | Twice the Normal level. Used where recent quality history has deteriorated. |
Glossary "S"
Sampling Proceedures PDF.
Example
Online Sample Size calculator.
With a "Batch Size" of 600 units, Normal Level II and 1.5% Acceptable Quality Level, the sample sizes found using the Online Calculator are shown below:
Single Sampling
Sample size = 80 units. 3 or less = Accept. 4 or more = Reject.
Double Sampling
1st. Sample size = 50 units. 1 or less = Accept. 4 or more = Reject. 2/3 = resample.
2nd. Sample size = 50 units. 4 or less = Accept. 5 or more = Reject.