Chapter 10

IN THIS CHAPTER

**Introducing hypothesis tests**

**Testing hypotheses about means**

**Testing hypotheses about variances**

**Visualizing distributions**

Whatever your occupation, you often have to assess whether something new and different has happened. Sometimes you start with a population that you know a lot about (like its mean and standard deviation) and you draw a sample. Is that sample like the rest of the population, or does it represent something out of the ordinary?

To answer that question, you measure each individual in the sample and calculate the sample’s statistics. Then you compare those statistics with the population’s parameters. Are they the same? Are they different? Is the sample extraordinary in some way? Proper use of statistics helps you make the decision.

Sometimes, though, you don’t know the parameters of the population that the sample came from. What happens then? In this chapter, I discuss statistical techniques and R functions for dealing with both cases.

A *hypothesis* is a guess about the way the world ...

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