Allow me to explain why.
Design by Contract? Good luck finding any empirical studies on it.
Code Review? Okay this one is actually really effective
* $thing only helps in specific contexts
* The benefits are minor at best
There are some things we know have obvious, overwhelming impacts in ALL kinds of fields.
Things like sleep.
On the other hand, we have precious few tool/method studies that all find no benefit or are inconclusive.
...Except for code review. That still holds up.