You may have asked yourself the question Am I in an average family? Other issues aside, the average number of people per family in the United States in March 1993 was 3.16 people. Depending on how you define 0.16 people, this is a pretty hard statistic to match. Average, in this sense, is identical with arithmetic mean; that is, the total of all items in a number of groups divided by the number of groups. Suppose that there are 25 families and that the sum of all the people in the 25 families is 79. Then the arithmetic mean for the number of people per family is 79/25 = 3.16 (the average number of people per family).
1
You may have had in mind a more meaningful statistic, however, when you considered the above question; that is, Does the number of people in my family match the number of people in a mode family? The mode is the most frequently occurring group. For example, suppose that 79 people in 25 families are distributed in the following manner:
People per family
2
3
4
5
Number of families
10
6
4
5
25 families total
Number of people
20
18
16
25
79 people total
2
The most frequently occurring family is the 2-person family with 10 occurrences. Therefore, the mode family is the 2-person family.
3
Then again, you may wonder if the number of people in your family matches the median family. The median is the group with the number of cases above it equal to the number of cases below it. In our example, the qualities above and below refer to the number of people per family. Suppose that you make a list from 1 to 25 of the families shown above from the lowest number of people per family to the highest number of people per family: from 1 to 10 the list consists of 2-person families; from 11 to 16 the list consists of 3-person families; from 17 to 20 the list consists of 4-person families; and from 21 to 25 the list consists of 5-person families. The median point of this list the 13th entry, because there are 12 entries before it and 12 entries after it. Since the 13th entry is a 3-person family, the median family is the 3-person family.
