# What is the correct way of comparing two very small groups (N = 3)?

I have 3 samples of water contamination (bacteria/L) from a lake which I want to compare to another, more "pristine" lake. So I have 6 values in total, 3 belonging to each lake:

contamination,  lake type
7576.48,        pristine
7472.81,        pristine
7511.55,        pristine
6803.65,        test lake
6692.63,        test lake
7128.27,        test lake


What is the best test to compare them? In the boxplot they look different. Initially I thought about a Student-t test, but with N = 3 it looks like it will be rather poor, right? Should I go then directly for the Wilcoxon rank sum test instead? Or what do you do when you have just 3 cases for each group?

• Also relevant: 1 2 – Gala Jul 2 '13 at 13:53