Comparing groups of projects done both with typical and Cleanroom SE:

Typical (traditional) productivity was measured at:
121 lines of code per person per month.

Cleanroom productivity was measured at:
559 lines of code per person per month.
(which was measured at 370 lines of code per person per month for the  first increments and 584 lines of code per person per month for later increments, as people became more experienced.)
 

The "quality" measured by a FQT (Formal Qualification Test) went from:
Typical SE: group of projects went from 23 to 27 failures per KLOC (thousand lines of code)
Cleanroom SE: 1.0 failures per KLOC
 

Evaluating productivity increases plus cost of fixing failures, for both groups of projects (traditional and Cleanroom) the calculated "Return On Investment" (ROI) was between 20.3 to 1 up to 50.5 to 1.

Important benefits were:

• Improved productivity
• Improved quality
• High staff morale