This is often a dramatically difficult task for those who have little experience in statistics. Luckily there are some good online resources to help you choose.
A quick general overview can be found here.
Here is a great resource from the biological sciences
Here is another from a social science perspective.
Remember that there are no cookbook recipes for conducting statistical analysis, you should always view each test critically and evaluate for yourself if your situation corresponds to the particular set of assumptions associated with your test of choice. Pages like the ones given above are general guidelines and should not be construed as hard and fast rules.
If you are still unsure, why not go ahead and post a question on our forum. Reading through the contents of one of the above pages should put you in a better position to ask directed question, and get a useful answer.
If you're still having trouble with this topic feel free to start a thread on the forum, and be sure to check out our guidelines for efficient posting.
The true ideals of great philosophies always seem to get lost somewhere along the road..
I had been wondering when someone might post this. We get some many "which test should I use" questions.
This UCLA page is also quite useful, and links to data analysis examples in SAS, Stata and SPSS.
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