One of the simplest yet still quite useful graphs is the *strip chart* (called a “dot plot” by some analysts). This graph provides a way to view how a set of numbers is *distributed*. That is to say, what is the shape of the data? Can we identify what the maximum and minimum numbers are, how spread out they are, and whether some of the numbers cluster together?

Let’s examine the `trees`

dataset provided with base R. To see a description of this data, type the following:

> ?trees

A new window opens, describing the data. Following is the information provided in the window:

- Description
- This is a brief narrative about the data.
- Usage
- This displays the dataset name.
- Format
- This explains that the structure is a data frame and that it has 31 observations with 3 variables, and gives the variable names and the units of measurement.
- Source
- This indicates where the data came from.
- References
- This gives examples of books or articles in which an analysis of the data appears. I sometimes copy and paste a reference into a search engine to see such an analysis. This does not always work, but when it does, it is usually very helpful.
- Examples
- This gives some R code using the dataset. It is sometimes very interesting to copy and paste one or more of the examples into the R console and see what kinds of statistical analyses and/or graphs are produced. In this particular case, the kinds of plots produced will be discussed later in the book, but there is also some ...

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