I can think of selection bias effects both in-favor of more defects and against it. On one hand, Haskell or Clojure probably attract more academic types who ha

I can think of selection bias effects both in-favor of more defects and against it. On one hand, Haskell or Clojure probably attract more academic types who have a reputation for (consistent with my experience) on-average worse-quality code. On other hand, the barrier-to-entry for these languages is higher so they tend to be programmed by more experienced folks. I assume that people pick functional languages in part because they believe the functional paradigm leads to higher-quality code, so the sample probably cares more about code quality to begin with.