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  Introduction a binary variable a nominal variable an ordinal variable a scale variable
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• Two variables - paired
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Analysing a binary vs. scale variable

Visualisation: Split histogram

To visualise the sample data between a binary and a scale variable various options exist, but two commonly used ones are a side-by-side box plot and a split histogram. For each of these options something can be said. The side-by-side box plot is a visualisation of some descriptive measurements, and therefor a bit more technical.

For the example used on the previous page, I'll use a split histogram such as the one shown in Figure 1.

Figure 1. Gender vs Grade for course.

The number of bars (bins) can change the look of this. There are various formal rules on how many bars there should be, and even more rule of thumbs. I recommend using between 5 and 12 bars. In this example I've used 8.

From Figure 1 we can see that it appears that the female students where split on the grade for the course (which explains the higher standard deviation), while the male students were less varied in their opinion. To find out if the average (mean) score of the female students, is significantly different from the male students, we will need to use a statistical test. This will be the topic of the next section.

As mentioned earlier an alternative visualisation is to use a box-plot

Binary vs Scale

Introduction

Impression

Visualisation

Test

Effect size

Reporting

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