They took 20,000 pages, split them into test and control groups, and changed the title of questions in the test group from "$QUESTION - Coderwall" to "$QUESTION

They took 20,000 pages, split them into test and control groups, and changed the title of questions in the test group from "$QUESTION - Coderwall" to "$QUESTION (Example) - Coderwall". They then measured how many more clicks the test group got compared to the control group.