(To help you remember what the median is, think of the median that is in the middle of the road.) The first step in
finding the median is to arrange the data in either decreasing or increasing
order. Let's arrange the mathematics test scores for two classes in increasing
order.
Class 1: 49, 54, 55, 65, 76, 76, 76, 78, 78, 81, 83, 85, 88,
89, 89, 90, 90, 91, 93, 99
Class 2: 55, 59, 60, 65, 68, 76, 77, 77,78, 80, 80, 80, 89, 89,
90, 92, 92, 95, 96, 98
Since there are 20 test scores for each class, there are two
"middle" scores, the tenth and the eleventh. We average the tenth and eleventh
scores to find the median.
(Median for Class 1)
(Median for Class 2)
Based on the medians, it appears that Class 1 did better than
Class 2 on the mathematics test. Also, notice that the median for Class 1 (82)
is not equal to an actual score from Class 1. Thus, if there is an even number
of scores, the median may not be equal to an actual score from the
data.
Do you think the median is affected by extreme scores like the
mean is?
