Chapter 4

IN THIS CHAPTER

Meeting conditions

Understanding that the median is the message

Getting into the mode

Statisticians deal with groups of numbers. They often find it helpful to use a single number to summarize a group of numbers. Where would a single summary number come from?

The best bet is to find a number that’s somewhere in the middle and use that number to stand for the whole group. If you look at a group of numbers and try to find one that’s somewhere in the middle, you’re dealing with that group’s central tendency. Like good ice cream, central tendency comes in several flavors.

## Means: The Lore of Averages

Just about everyone uses averages. The statistical term for an average is mean. Sometime in your life, you’ve undoubtedly calculated one. The mean is a quick way of characterizing your grades, your money, or perhaps your performance in some task or sport over time.

Another reason for calculating means concerns the kind of work that scientists do. Typically, a scientist applies some kind of procedure to a small sample of people or things and measures the results in some way. He or she uses the results from the sample to estimate the effects of the procedure on the population that produced the sample. As it happens, the mean of the sample is the best estimate of the population mean.

### Calculating the mean

You probably don’t need me to tell you how to calculate a mean, but I’m going to do it anyway. Then I show you ...

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