Studying individuals is the wrong experiment. Static typing benefits tooling most when you have larger groups of programmers who much collaborate, often asynchronously. It's easy to hold a mental model of the code you write in your head and minimize mistakes, it's harder to hold a mental model of a larger program consisting of code written by many programmers.

I'd like to see them hand a pre-written codebase of say, 10,000 lines to a bunch of students, and ask them to make large changes/new features to the codebase.