The Mean Absolute Deviation (MAD) of a set of data is the average distance between each data value and the mean. The mean absolute deviation is the average of the positive distances of each point from the mean. The larger the MAD, the greater variability there is in the data (the data is more spread out). The MAD helps determine whether the set's mean is a useful indicator of the values within the set. The larger the MAD, the less relevant is the mean as an indicator of the values within the set. Let's compare Sherlock's data set with that belonging to Watson. to see what the Mean Absolute Deviation (MAD) tells us.