...

• Some tasks may be confusing or misleading.
  This is especially likely if you didn’t properly pilot your test. Some tasks are hard to phrase clearly without giving away the answer, but remember that a confusing task is a problem in your study, not necessarily a problem in the tree itself. You shouldn’t change the wording during the test, but you should revise in your next round of testing.
  
  
• Some correct answers aren’t marked as “correct”.
  After doing hundreds of tree tests, we still run into this wrinkle all the time. When we set up each task, we try to mark all the correct answers for it. However, in a large tree, each task may have several correct answers, and it’s likely we’ll miss a few.
  Because of this, a good testing tool should let you (as the test administrator) change which answers are correct for each task, either while the test is running or afterward when you’re doing your analysis. We often find that test scores go up substantially when we do this post-test correct. For more on this, see Chapter ~, Analysing Analyzing Results.
  
  
  

...