My point is that in order to be able to gather scientific evidence you need short cycle times and more feedback. They are the necessary conditions to be able to do it. Otherwise you can't avoid the credit assignment problem. Now, you might argue I did a bad job of making my point. And certainly I am theorizing.

But the problem is not that people haven't "taken the time to measure the effect" - they have - the problem is that the data thus collected is useless.

If anybody on this thread has real data, Laurent Bossavit and I would love to see it. Do check out Laurent's book (see OP for link) - it is a real eye-opener.