Chapter 6

Getting the Picture: Graphing Categorical Data

In This Chapter

arrow Making data displays for categorical data

arrow Interpreting and critiquing charts and graphs

Data displays, especially charts and graphs, seem to be everywhere, showing everything from election results, broken down by every conceivable characteristic, to how the stock market has fared over the past few years (months, weeks, days, minutes). We’re living in an instant gratification, fast-information society; everyone wants to know the bottom line and be spared the details.

The abundance of graphs and charts is not necessarily a bad thing, but you have to be careful; some of them are incorrect or even misleading (sometimes intentionally and sometimes by accident), and you have to know what to look for.

This chapter is about graphs involving categorical data (data that places individuals into groups or categories, such as gender, opinion, or whether a patient takes medication every day. Here you find out how to read and make sense of these data displays and get some tips for evaluating them and spotting problems. (Note: Data displays for numerical data, such as weight, exam score, or the number of pills taken by a patient each day, come in Chapter 7.)

The most common types of data displays for categorical data are ...

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