Chapter 4. Dot Charts
Basic Dot Chart
The dot chart (sometimes called “dot plot”) is quite similar to the strip chart in that it shows how spread out or clumped together points are. But the dot chart goes beyond this and gives us the opportunity to glean even more information from our data. You might consider the next dataset a bit gruesome, but consider that some readers of this book might indeed deal with this kind of data on a regular basis. Because the methods introduced in this book can be applied to a wide range of subjects, for readers with varying needs, diverse types of data have been chosen to illustrate the use of graphs. So, let’s look at the USArrests dataset, which gives arrest rates per 100,000 population for serious crimes in each of the US states in 1973:
> attach(USArrests)
> head(USArrests) #shows first 6 rows, can get all with:
USArrests
Murder Assault UrbanPop Rape
Alabama 13.2 236 58 21.2
Alaska 10.0 263 48 44.5
Arizona 8.1 294 80 31.0
Arkansas 8.8 190 50 19.5
California 9.0 276 91 40.6
Colorado 7.9 204 78 38.7
This dataset includes values for four named variables. There is also one column without a variable name in the top row. The values in the lefthand column are row.names—in this particular case, the names of states. Many times, the row name is simply a number.
Let’s explore this dataset. First, see what a strip chart can tell you about murder arrests. Try it and ponder what you have learned about murder arrests from the strip chart. Are the arrest ...