pedrofurla.github.com
Empirical studies on the impact of type systems
An Empirical Study of the Influence of Static Type Systems on the Usability of Undocumented Software
A QUANTITATIVE ANALYSIS OF WHETHER UNIT TESTING OBVIATES STATIC TYPE CHECKING FOR ERROR DETECTION
A overview of the conclusion in a blog post by the author:
Unit testing isn't enough. You need static typing too.
And answered by Rafael Ferreira
Types and Bugs
An experiment about static and dynamic type systems: doubts about the positive impact of static type systems on development time
Suggestions and other works are very welcome. (It's github, you know how to contact me)