I think methodically you'd need equivalence testing for that. Your hypothesis would be that productivity is equal (enough) and you could then discuss the additional benefits of TDD.
I can't remember if I read a study like this for TDD but equivalence testing is fairly underused outside of pharma/medicine (it's often even called bioequivalence) where the test usually shows similar enough effects and the extra benefits are cost savings (for generics).
I can't remember if I read a study like this for TDD but equivalence testing is fairly underused outside of pharma/medicine (it's often even called bioequivalence) where the test usually shows similar enough effects and the extra benefits are cost savings (for generics).