[pomatius]

...and attitudes like these are why most Software Engineering theory is BS. We refuse to measure things in a reproducible way, and would rather stick with subjective pre-scientific concepts such as "clean code" and hit-or-miss rules of thumb for project estimation. You need an objective way of measuring and testing whether your hypothesis (be it that clean codes improves maintainability, or that X strategy is reducing dev churning) is true, and good KPI's are that.