TDD: Adequate Training

From "The Effects of Test-Driven Development on External Quality and Productivity: A Meta-Analysis", by  Y. Rafique and V.B. Misic (Ryerson University, Toronto, Canada):

"We note a few key issues that the authors of future empirical studies should be aware of when designing their experiments. Adequate training should be given to the subjects so that they can sufficiently grasp the TDD technique prior to the actual experiment. Detailed information about training should be provided as well, including specific areas as well as the duration of the training."

Does this mean that TDD is too difficult to learn?