Chapter 7

Going by the Numbers: Graphing Numerical Data


Bullet Making and interpreting histograms and boxplots for numerical data

Bullet Examining time charts for numerical data collected over time

Bullet Gaining strategies for spotting misleading and incorrect graphs

The main purpose of charts and graphs is to summarize data and display the 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, including 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 numerically ...

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