How Charts Lie

Lecture 14

Dr. Benjamin Soltoff

Cornell University
INFO 3312/5312 - Spring 2024

March 16, 2023

Announcements

Homework 3 distributed tomorrow
Individual projects due end of the month

The 2016 electoral results

The stereotypical chart

What does this chart tell us?
What is misleading about the chart?

A more honest approach

An even more honest approach?

Bubble map

Which is more correct?

Neither

Not an adequate representation of the number of votes each candidate received

Only includes votes for the winning candidate

Better?

Electoral votes

Charts that lie by…

Being poorly designed
Displaying dubious data
Displaying insufficient data
Concealing or confusing uncertainty
Suggesting misleading patterns

…by being poorly designed

Truncated axes

Truncated axes

Democrats do it too

Truncated \(y\)-axis

Truncated \(x\)-axis

3D charts

2D versions

Planned Parenthood

Planned Parenthood

Planned Parenthood

Planned Parenthood

National guidelines for the frequency of cervical cancer screenings were officially changed in 2012, but the American College of Obstetricians and Gynecologists started advising a reduction of frequency in 2009. Previously, women received a pap smear to screen for cervical cancer once a year, but it is now recommended that pap smears should be performed every three years.

Baseline of zero

Baseline of zero

Meaningless (or not) zero baseline

Meaningless (or not) zero baseline

…by displaying dubious data

Gender wage gap

Gender pay gap

Gender pay gap

What causes the pay gap?

Porn in red states

Where’s Kansas?

Who pays for porn?

…by displaying insufficient data

Immigrants and crimes

Is this high or low?

As Attorney General Jeff Sessions announced the end of the Obama-created Deferred Action for Childhood Arrivals (DACA), from which more than 800,000 un-vetted young illegal aliens have been given protected status and work permits, the number of them who are convicted criminals, gang members, or suspects in crimes remains staggering.

What is a reasonable comparable? Entire U.S. population

Immigrants and crimes

Tax cuts (again)

What’s an average family?
How many families are similar to the average?

Normally distributed household incomes

Actual distribution of household incomes

Distribution of tax benefits

Box office revenue

Box office revenue

Unadjusted variables

Adjusted values

Don’t assume geographic data needs a map

…by concealing or confusing uncertainty

Election polling

Uncertainty

Uncertainty vs. a mistake
Confidence interval
- Margin of error
- Confidence level

Visualizing uncertainty

FiveThirtyEight

…by suggesting misleading patterns

Watch out for fallacies

Correlation does not equal causation
Amalgamation (Simpson’s) paradox

A trend appears in several groups of data but disappears or reverses when the groups are combined
Ecological fallacy

A logical error that occurs when the characteristics of a group are attributed to an individual
Omitting known unknowns