At the ESCOM conference a few years ago I heard about the Ollen Musical Sophistication Index (OMSI), which is a ten-question standardised test for evaluating musical skills. The test is the result of the PhD dissertation by Joy Ollen.
When I first read about this test, I thought it would be interesting to have an interactive version available to use in studies. Fortunately, now I see that there is an online version available at the MARCS Auditory Laboratories,