Link To Full Story: www.seomoz.org
What went wrong?
As far as I can tell, the experiment was executed without a problem. As it turned out, the problem wasn't necessarily with the experiment itself but rather with interpreting the results. I used the wrong metric to evaluate the results (average rank of each testing group) and relied on too few samples.
What is the new test?
Rather than testing which PageRank sculpting method works the best, I am now going to test if the nofollow method works at all.
We ran the numbers (see math below) and found out we could run this test in either of two ways. The first way would only require 40 samples but would require a very high rate of success (nofollow beating control) to prove valid. The second test emphasizes precision and requires a much lower success rate but a much larger sample.
I have both tests planned and would love to hear your feedback of the tests prior to running them. Below is a diagram of the plan to test the nofollow method against a control (null) case.
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