De Rerum Natura

I have applied the autonomous difference equations to test the quality of ten out of twenty questions I used in a Physics exam I gave in the Spring of 2006 to an introductory class for engineering students. That dark square in position six of the matrix corresponds to the question least likely to be answered correctly. Only 64 students out of 250 answered correctly. The reason this happened was that I gave a very clever wrong answer that attracted most of the students (the correct answer but forgetting to take a square root). I have used the precision error covariance matrix to assess the test maker not the students!

This example also highlights the general applicablity of the precision error covariance matrix. There now exist two experimental verifications of its usefulness: digital elevation maps and test assessment.