What Is Data?

Before we start to describe some of the basic tools that you can use to explore your data, we should agree on what we mean when we use the word “data.” It would be easy to write an entire book about the possible definitions of the word “data,” because there are so many important questions you might want to ask about any so-called data set. For example, you often want to know how the data you have was generated and whether the data can reasonably be expected to be representative of the population you truly want to study. Although you could learn a lot about the social structure of the Amazonian Indians by studying records of their marriages, it’s not clear that you’d learn something that applied very well to other cultures in the process. The interpretation of data requires that you know something about the source of your data. Often the only way to separate causation from correlation is to know whether the data you’re working with was generated experimentally or was only observationally recorded because experimental data wasn....