Up until now it has mostly been opinions and biases and even though many popular programmers[1] have been saying this for a very long time, it's great to see a controlled study done about it.

This makes it a fact and a great counter argument for helping a lot of programmers who are being forced to practice TDD because of the generally accepted claims in productivity and code quality associated with doing it.

[1] http://david.heinemeierhansson.com/2014/tdd-is-dead-long-liv...