Mean
The mean is the arithmetic average, of a set of scores. You are probably more familiar with the mean than any other measure of central tendency. You encounter the mean in everyday life whenever you calculate your exam average, batting average, gas mileage average, or a host of other averages.
The mean of a sample is calculated by adding all the scores together and dividing their sum by the number of scores.
Exam Scores: 99, 92, 93, 94, 97
The mean (represented as M in APA publications) for the above data is (99 + 92 + 93 + 94 + 97)/5 or 95.
Since each score contributes to the value of the mean, extreme scores affect its value.
Suppose a book publisher is interested in the number of books sold by two different representatives, Mr. Smith and Ms. Johnson. The publisher might collect the number of books sold by each representative for each of several months and then compare their means. Hypothetical data for this example are shown in Table 2 below.
Table 2.
|
Month |
Smith |
Johnson |
|
Jan |
12 |
8 |
|
Mar |
13 |
7 |
|
May |
12 |
2 |
|
July |
14 |
20 |
|
Sept |
11 |
21 |
|
Nov |
13 |
17 |
|
M |
12.5 |
12.5 |
Surprisingly, both representatives sell the same number of books per month, on average.
Learning Check #6:
What is the mean number of brothers and sisters listed in Learning Check #5?