Measure productivity of the same people working different numbers of hours per week? (And the study needs to run longer than one week at each number of hours. Working overtime boosts your productivity - the first week.)
How do you measure the productivity of cognitive work over an entire week? It's kind of subjective, and having the subjects self-report their level of satisfaction would probably be unreliable.
EDIT: I guess the trick might be to not use a survey, but to give the participants all the same project to work on (very expensive), then adjust the results based on their previous performance. I think an ideal group for this would be students because they're all already working on the same projects. Tell one (random) group that they can have some money if they promise to work on their class project for no more than one hour a day. Could this work?
EDIT: I guess the trick might be to not use a survey, but to give the participants all the same project to work on (very expensive), then adjust the results based on their previous performance. I think an ideal group for this would be students because they're all already working on the same projects. Tell one (random) group that they can have some money if they promise to work on their class project for no more than one hour a day. Could this work?