Bars and dots: point data

Visualization Best Practices in R

Nick Strayer

Instructor

What is point data?

  • One categorical axis, one numeric
  • Counts, averages, rates, etc.

Visualization Best Practices in R

A single observation

  • Represents a singular observation of something
  • E.g. population of a state, rate of cell growth

Visualization Best Practices in R

The bar chart

  • Popular
  • Simple
  • Accurate 
ggplot(who_disease) +
  geom_col(aes(x = disease, y = cases))
Visualization Best Practices in R

Visualization Best Practices in R

Not always the best

  • Bar charts are frequently used when other charts are more appropriate
  • A few principles can be followed to help avoid this

Visualization Best Practices in R

The stacking principle

  • Should be used for data that represents a meaningful quantity
  • Ask: 'Could I stack what I'm measuring to make the bars?'

Visualization Best Practices in R

Why quantities?

"...viewers judge points that fall within the bar as being more likely than points equidistant from the mean, but outside the bar..."

               - Scholl & Newman, 2012

 

  • People view the bar as 'containing' the values below top
  • Quantities fulfill this assumption

Visualization Best Practices in R

A big deal?

  • Not really...
  • ... but alternatives are not worse, so they may as well be used

 

Visualization Best Practices in R

Let's practice!

Visualization Best Practices in R

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