sampling

[michimichi]

hi, can anyone help me,
how can many samples should i take in order to have a representative sample of 500 items/samples?
can u also give me a formula?

[michimichi]

edit,
how many samples should i take in order to have a representative sample of 500 samples/items? im using a random sampling

[JorgeLobo]

Can;t answer without understanding the test objective (your sampling for purpose - not just for the sake of getting samples) and dynamics invovled. Can you be more explicit?

[JorgeLobo]

Sorry michi - there really is no pat answer. Factors such athe anticipated importance, frequency and distribution of the character you expect to measure/detect will dictate the statistical confidence your sampling.
There would be differences, for example, between sterility testing of a injectble drug product and analysis of water samples from a city.
Can you tell us what you are trying to find or measure and it's nature?

[michimichi]

i have 500 packs of tuna in one container van, i only need 1 pack to be delivered to the lab for chemical and micro analysis.
.The pack that i will transfer should be a composite sample from the 500 packs in the van.so how many packs should i be getting in order to get 1.?

[JorgeLobo]

Have you looked at FDA BAM?
http://www.fda.gov/Food/ScienceResearch ... 063335.htm

[JorgeLobo]

michi - did this help?

[michimichi]

ya, thanks