Page 119 - Statistics for Dummies

Chapter 7
Going by the Numbers:
Graphing Numerical Data
In This Chapter
▶ Making and interpreting histograms and boxplots for numerical data
▶ Examining time charts for numerical data collected over time
▶ Strategies for spotting misleading and incorrect graphs
he main purpose of charts and graphs is to summarize data and display
Tthe results to make your point clearly, effectively, and correctly. In this
chapter, I present data displays used to summarize numerical data — data
that represent counts (such as the number of pills a patient with diabetes
takes per day, or the number of accidents at an intersection per year) or
measurements (the time it takes you to get to work/school each day, or your
blood pressure).
You see examples of how to make, interpret, and evaluate the most common
data displays for numerical data: time charts, histograms, and boxplots. I also
point out many potential problems that can occur in these graphs, includ-
ing how people often misread what’s there. This information will help you
develop important detective skills for quickly spotting misleading graphs.

Handling Histograms

A histogram provides a snapshot of all the data broken down into numeri-
cally ordered groups, making it a quick way to get the big picture of the data,
in particular, its general shape. In this section you find out how to make and
interpret histograms, and how to critique them for correctness and fairness.

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