Basic statistics

This chapter covers

■Descriptive statistics

■Frequency and contingency tables

■Correlations and covariances

■t-tests

■Nonparametric statistics

In previous chapters, you learned how to import data into R and use a variety of functions to organize and transform the data into a useful format. We then reviewed basic methods for visualizing data.

Once your data is properly organized and you’ve begun to explore the data visually, the next step is typically to describe the distribution of each variable numerically, followed by an exploration of the relationships among selected variables two at a time. The goal is to answer questions like these:

■What kind of mileage are cars getting these days? Specifically, what’s the distribution of miles per gallon (mean, standard deviation, median, range, and so on) in a survey of automobile makes and models?

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