The coefficient of variation (CV) is the ratio of the standard deviation to the mean. The higher the coefficient of variation, the greater the level of dispersion around the mean. It is generally expressed as a percentage. Without units, it allows for comparison between distributions of values whose scales of measurement are not comparable. When we are presented with estimated values, the CV relates the standard deviation of the estimate to the value of this estimate. The lower the value of the coefficient of variation, the more precise the estimate.
Second, we examine the distribution of results within classes. In the absence of external controls, the teacher can communicate the correct answers to students or change their answers in the answer sheet, or students can simply copy from each other. If outright cheating by students and/or teachers was taking place in the classes without the external examiner, we should find that in these classes – ceteris paribus - the standard deviation and the coefficient of variation of test results are lower than in classes with the external examiner, where cheating is minimized or altogether absent (Bertoni, Brunello and Rocco, 2013: 74).