If you are trying to measure the ability to critically evaluate material and apply it to a question at hand keep in mind that creativity is not something that can be forced easily.

There are students who are good at giving pretty good answers very fast. Others have what I call slow intelligence. They will systematically come up with better solutions but they require more time to do so.

I have found take home exams to sometimes be a solution. When I give a "take home" I always make the students take a supervised exam also. (70% take home and 30% for the supervised part). Some students tend to "consult each other" on the take home and the supervised part provides a way to adjust.

Gilbert