Additional hypothesis: the result of this test depends strongly on which one you are more familiar with and which one you prefer. If I hate writing Cobol, I'm going to spend that part of the test pining for the other language and not using whatever the up-to-date idioms are for making Cobol manageable, but just fighting Cobol until I can switch to the language I really wanted to use.

So, anyone doing this should consider trying to get a sample of people who are more or less indifferent between the options, so they don't sabotage the test