Ask HN: Moving from hand-waving about software development to empirical data?

"The Mythical-Man Month" recently came up in a conversation and I realized that a 40 year old tome is still one of mainstream development's primary references. Despite this, the software industry is dominated by fads, trends and cargo cults, without any way of measuring the value they add, if any. Consultants are especially likely to push change for its own sake. Is it possible to define and measure improvement? How?