2022 Introduction to Statistics in Research Mitchell 2nd ed

I N T R O T O R E S E A R C H : D A T A V I S U A L I Z A T I O N & C O M M O N S T A T T E S T S

Bar Chart

A bar chart is a good way to display categorical data.

Example : You are doing an observational study in Indiana. The U.S. Department of Transportation has issued guidelines that say helmets should reach the bottom of the motorcyclist's ears. You decide to do an observational study at a several key crossroads. Each time a motorcyclist passed you recorded the following categories: 1) no helmet; 2) non-compliant helmet; and 3) compliant helmet.

Table 78Showing the use of Frequency in a chart

The table is called a frequency distribution. Essentially, it displays the possible categories along with the associated frequencies or relative frequencies. Relative frequency is the proportion of observations.

Relative Frequency by the formula: relative frequency = frequency ÷ number of observations

Table 79: Demonstrating the relative frequency

Comparative Bar Chart

Comparative bar charts can be used to provide a visual comparison of univariate, categorical data for two or more groups. Here are the key points.

1. Use color-coded columns to indicate which bars correspond to each group. 2. Use relative frequencies on the vertical axis instead of the frequency (count). The use of relative frequency helps make a more meaningful comparison even if the same sizes are not the same.

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