[willtim]

What numbers do you require? If there was a metric measuring simplicity then Lisp (or perhaps a modern variant, Scheme) would probably win - it is a local optimum of language design, essentially just lambda calculus exposed via a very simple grammar (which aids meta-programming).

[oblio]

Any kind of serious study will do :)

[willtim]

Such studies are very hard to do, it is almost impossible to factor out social preferences. For me personally, I am most productive in languages like Haskell and OCaml.