Is there evidence that using dynamic languages has an impact on productivity?

I am wondering if there are any experiments that show the existence or the non-existence of a correlation between usage of a dynamic language (such as Python, Ruby, or even languages that run on the Java platform such as Groovy, Clojure) over a static language (such as C/C++), and the difference in the productivity.

While I'm not aware of research on productivity, there's been research on comprehension. Philip Wadler has been collecting links to papers on this topic: see this post and this one.

StackExchange Computer Science Q#1150, answer score: 11