I have to test the the effect of two different treatments on a set of samples. On the surface, this seems an obvious option for a two sample test. The problem is that the samples being treated are all drawn from the same pool.
Let's say I have a pooled volume of a fluid. I can draw 20 samples from this pool - 10 will be treated with method A and 10 will be treated with method B. Can I still use a two-sample test such as a t-test or a Mann-Whitney test for the two sets? Does this violate the assumption of independence of the samples because they all come from the same pooled volume, or is the fact that they are treated independently enough?
Adding content from comments below to help clarify the question a bit.
Sticking with the pharma theme, let's say I've collected 20 ml of blood from a single person, and I split that into 20, 1 ml samples to test two drugs - 10 samples treated with drug and 10 untreated. All 20 were derived from the same person, but tested individually. This is compared to collecting samples from 10 individuals and splitting the samples so that I have 10 treated and 10 untreated in a paired design.
I'm concerned that the original design (20 ml from a single individual) violates independence, but I'm not certain that the comparison is invalid.