Sociology 393 Lectures

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Mean

The mean is often called the average.  It is the arithmetic middle.  You can calculate the mean by adding up the values of all cases and then dividing by the total number of cases.

The mean, therefore, only works if you have measurement data.  Otherwise, adding up values would be meaningless.  For example, I might want to find the mean years of education for a sample of 10 immigrants to the United States.  The years of education for the 10 immigrants are 10, 11, 11, 12, 12, 12, 12, 16, 16, and 20.  To find the mean I do the following:

However, because the mean relies on adding up the values of all the cases, extremely low or high cases can influence it greatly.  For example, if there was an eleventh immigrant in the example above who happened to have no formal education, he or she would lower the mean considerably.

A few extreme values (outliers) can make the mean unreliable as a measure of central tendency.  In such cases, we generally rely on the median as a measure of central tendency.

SPSS instructions for finding the mean

SPSS instructions for comparing means of different groups

 

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Last Updated: January 19, 2005