> Are there actual facts to back up claims to productivity boosts or failures with a given paradigm across large numbers of programmers and organizations?
NO. Functional people claim that, but never had a proof, since there aren't that many people using it to build large systems. Thus this myth lives on. :)
Actually most of us do not have a choice, OOP languages, tools and frameworks are usually forced upon us. At least OOP languages are finally adopting functional features, but if one really wants to favour immutability and composition (modern OOP advice), one needs a functional-first language.
NO. Functional people claim that, but never had a proof, since there aren't that many people using it to build large systems. Thus this myth lives on. :)