There is a lot of interest in research on the benefits of static vs dynamic typing. But unfortunately there is not a lot of hard data. There were some experiments, e.g.
http://dl.acm.org/citation.cfm?id=2047861
which seem to support the claim that dynamic typing is better for rapid prototyping. So if you have data that correlate typing disciplines with bug rates, it would be hugely valuable to share it.
On the other hand, there's the 1994 Navy sponsored study which had as an (informal) conclusion that Haskell was better at rapid prototyping when compared to other languages of the time.
The experiment mostly compared Haskell with imperative languages such as C++ and Ada, but there was also at least one Lisp variant. There were several informal aspects to the study, not the least of which being that there were no clearly defined requirements for the system to be implemented (so it was up to each participant to define the scope), but the conclusion is very interesting nonetheless:
The Haskell took less time to develop and also resulted in less lines of code than the alternatives, and it produced a runnable prototype that some of the reviewers had a hard time believing wasn't a mockup. Many of the alternatives didn't even end up with a working system. It should also be noted that the Haskell participants decided to expand the scope of the experiment; i.e. they didn't "win" because they implemented a heavily simplified solution, but in fact added extra requirements to their system and still finished earlier!
Even though Obj-C wasn't included in the study, there were similar enough C-like languages in it, so my bet is that Haskell would have won against it as a rapid prototyping language as well.
They used Java as the static language, which is relatively cumbersome as far as statically typed languages go, and is also known for its verbosity. "Rapid prototyping" and "java" does not really mesh to begin with, or at least that's what the common wisdom tends to say.
It seems that they need another survey/study to check the OPs claim (namely do some research on productivity in languages with stronger static type systems than java).
