Why do you use a sample when testing products?

Answer 1

Your only choice is to use a sample (part of the whole), or test every single product. If you're testing hand cream, and you don't use a sample, you would have to test everything the hand cream factory produced, leaving nothing to sell, driving profits into the ground.

The idea is that if a product comes from the same source, and is produced or grown under the same conditions, a sample will be identical to the whole. So if a sample tests to be Grade 'A' beans, the whole batch will most likely be Grade 'A'.

Of course there has to be a methodology behind the sampling. You can't just sample the first item off the production line, nor the last. Sampling has to occur during every phase of a production run to make sure conditions are the same from the beginning of the run, through the middle, to the end.

Sampling has to be 'random'. It might be possible to alter the sample if it is taken at the same time every time. For example if a sample is taken off of a production line 5 minutes before break time every day, workers could just put extra energy into the last product they assemble before break time. Or if a sample of grain is taken from the top of a farmers grain truck, he will make sure that all the garbage grain is at the bottom of the pile.