Misleading Graphs

1
Misleading Graphs
2
Questions to Ask When Looking at Data and/or
Graphs

• Is the information presented correctly?
• Is the graph trying to influence you?
• Does the scale use a regular interval?
• What impression is the graph giving you?

3
Why is this graph misleading?
4
This title tells the reader what to think (that
there are huge increases in price).
The scale moves from 0 to 80,000 in the same
amount of space as 80,000 to 81,000.
The actual increase in price is 2,000 pounds,
which is less than a 3 increase.
The graph shows the second bar as being 3 times
the size of the first bar, which implies a 300
increase in price.
5
A more accurate graph
An unbiased title
A scale with a regular interval.
This shows a more accurate picture of the
increase.
6
Why is this graph misleading?

• The scale does not have a regular interval.
• There is no label on either axis.

7
It is most important to display percentages
correctly in order for the graph not to be
misleading.
8
Graphs can be misleading in the news.

• The margin of error is the amount (usually in
  percentage points) that the results can be off
  by.
• Be wary of data with large margins of error.

9
From CNN.com
10
Problems

• The difference in percentage points between
  Democrats and Republicans (and between Democrats
  and Independents) is 8 (62 54). Since the
  margin of error is 7, it is likely that there is
  even less of a difference.
• The graph implies that the Democrats were 8 times
  more likely to agree with the decision. In
  truth, they were only slightly more likely to
  agree with the decision.
• The graph does not accurately demonstrate that a
  majority of all groups interviewed agreed with
  the decision.

11
CNN.com updates the graph
12
What to look for

• Be sure the vertical or horizontal scale starts
  at zero.
• Be sure both scales and intervals are consistent.
• Be sure the labels are correct.
• Make sure the percentages are displayed correctly
  on circle graphs.
• Be wary of large margins of error!

13
Now, lets practice! ?