Forum for Sampling Practices

A simple scenario here:

If a company imports vegetables and wants to conduct inspection , how to go about developing the sampling plan?

For instance,

There are 40 boxes of tomatoes. 1 box contains 1 kg of tomatoes.
How many boxes to take to sample?
How many tomatoes to sample in each box ? All?
(just inspecting for defect/no defect)
Often there is given a acceptance number does it refers to the number of tomatoes, or the boxes of tomatoes ?

The often used term lot size
does it refers to the boxes holding the tomatoes or every single unit of tomato can it be refered to the weight?

i have really no idea.

ihavereallynoidea wrote:The often used term lot size
does it refers to the boxes holding the tomatoes or every single unit of tomato can it be refered to the weight?

Lot size (N) refers to the total number of individual tomatoes.

The sample size (n) refers to the number of individual tomatoes in the sample.

You use the quality of the sample to make an accept/reject decision about the whole lot.

You should avoid taking all your samples from one box -- as that box would have a different history from some other box. The sample is best selected from among several boxes. If opening boxes is not difficult, or if the boxes are going to be opened anyway, you might as well collect the sample equally from among the boxes.

If opening boxes presents a problem, I have seen a balance struck between difficulty and accuracy by opening a number of boxes equal to the square root of n. For example n=36 tomatoes from 6 boxes. Then select about the same number of individual tomatoes from each box.

ihavereallynoidea wrote:Often there is given a acceptance number does it refers to the number of tomatoes, or the boxes of tomatoes ?

Acceptance number (typically called Ac or C) refers to the maximum number of defectives you can have in the sample and still accept the lot. For example, if the acceptance number of the sampling plan is 1, then if the sample contains one defective tomatoes then the whole lot is accepted. It there are 2 defective tomatoes then the whole lot is rejected.