Pattern of answer changes to multiple choice questions in physiology

The belief that it is unwise to alter the initial response to a multiple choice question is questioned.
Among 39 380 MCQ responses, there were 1818 changes (4.62%) of which 21.9% were correct to incorrect responses, 46.3% incorrect to correct responses and 31.8% incorrect to incorrect.
This effect was very much more marked among the better students, incorrect to correct changes accounting for 61% of the responses in the upper group, 42% in the middle group and 34% in the lower group.