2.6.Displaying & Describing Data

Plots and Tables

Bárbara D. Bitarello

2025-10-01

Outline

  • Wrap-up: Rules of data visualization - principles of good plots

Problem? 👎

Transform Data to Reveal Patterns 👍

Mistakes in displaying data:

  1. Displayig Magnitudes Dishonestly

Problem?

Presenting magnitudes dishonestly

  • This plot suggests that centers are 20X taller than guards.

How to represent magnitudes dishonestly: 👎

  • Start bar plots at a non-zero value

How to represent magnitudes honestly: 👍

  • Start bar plots at zero (if the variable starts at zero)

Why? The height of a bar plot makes us think in magnitudes.

Mistakes in displaying data:

  1. Draw elements unclearly

Problem? 👎

  • x-axis labels obscure one another.

👍 Flip Axes to Present Graphics Clearly

👍 Clear Graphics for Everyone

Consider your audience

Direct Labelling May Clarify Graphics

Labels directly on plots may also help with clarifying patterns

How to draw graphical elements unclearly: 👎

  • Unthinkingly accept default options from plotting programs

  • Do not consider how a diverse audience will consume your figure

How to draw graphical elements clearly: 👍

  • Reflect on plot design

  • Consider the diverse audience you are reaching and how they may interact with your plot

A note about boxplots

  • There is more than one way to define the whiskers in a boxplot

  • R (both base and ggplot) use the following. If there are no outliers, whiskers go up to max and min value

  • But how are outliers defined?

Case 1: If there are no outliers in the dataset

R uses the popular method of \(\text{lower fence}=Q1–1.5(IQR)\) and \(\text{upper fence}=Q3+1.5(IQR)\). If there are no values beyond these limits, it considers the dataset to not have outliers for the purposes of a boxplot:

Case 2: there are outliers

If there are outliers, whiskers go up to \(Q3+1.5IQR\) and down to \(Q1-1.5IQR\) and outliers are shown as circles

Case 2: there are outliers in the dataset. Whiskers defined by Q1–1.5(IQR) and Q3+1.5(IQR)

Please contribute!

A thread on plots that could use some TLC:

https://piazza.com/class/mekmad7xwqw14d/post/12

That’s all for today

Forrest says "And that's all I wanted to say about that"

From: makeameme.org