The effect of statistical moderation
The effect of statistical moderation can be shown in pictorial form. Two sets of diagrams are shown below, each contrasting the effects of different combinations of averages and standard deviations of marks.
Cases 1 and 2
If school marks for a course are on average lower, and more tightly bunched (smaller standard deviation) than the standardised WACE course examination marks of these students, then the school marks are moderated upwards and are more spread out.
Conversely, if school marks for a course are on average greater, and less tightly bunched (greater standard deviation) than the standardised WACE course examination marks of these students, then the school marks are moderated downwards and are less spread out.
Use your mouse to click and slide the standardised exam marks (oranges) and the school marks (apples) up and down the 0-100 scale to see the effects of statistical moderation.
Final mark is the average of the standardised moderated school mark and the exam mark.
Cases 3 and 4
If school marks for a course are on average higher, and more tightly bunched (smaller standard deviation) than the standardised WACE course examination marks of these students, then the school marks are moderated downwards and spread out further. If school marks for a course are on average lower, and have a standard deviation which is similar to that of the standardised WACE course examination marks, then the school marks are moderated upwards, and no change to the spread of the marks is required.
Use your mouse to click and slide the standardised exam marks (oranges) and the school marks (apples) up and down the 0-100 scale to see the effects of statistical moderation.
