Educational Psychology / Unit 13 EDP 1223 worked example, 60 to 90 seconds
Describing a Class's Scores
The idea
Describing a class's scores takes a center and a spread. The mean adds the scores and divides by their number; the median is the middle score in order; the mode is the most frequent. The range is the highest score minus the lowest, and the standard deviation gives the typical distance from the mean. When an outlier appears, the mean moves toward it and the median stays put, so the median then describes the typical student better.
In practice
Worked example: five scores are 70, 75, 80, 80 and 95. They add to 400, so the mean is 80; the median is 80; the mode is 80; the range is 25. Replace the 70 with a 20: the total falls to 350 and the mean to 70, the median stays 80, and the range grows to 75.
Where people slip
Always pair a center with a spread. The range rests on only two scores, which is why the standard deviation is the more stable measure of spread.
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