Editing graphics

1
Editing graphics
July 10, 2006 Bill Cloud University of North
Carolina at Chapel Hill
2
The agenda

• Game 1 Find the error.
• A quick look at graphics.
• Discussion How can we reduce errors?
• Game 2 Whats my question?

3
A good map or chart

• Is free of errors.
• Is easily understood by the readers.
• Makes good use of its allotted space.
• Is clearly connected to the story.
• Has text elements that complement, rather than
  repeat, accompanying headlines.

4
A good map

• Includes, in most cases, both a north pointer and
  a distance scale.
• Clearly labels the significant elements on the
  map.
• Labels streets and other landmarks mentioned in
  the story.

5
A good chart

• Presents information clearly without wasting
  space.
• Reflects changes in the value of the dollar.
• Reflects changes in the population.
• Appropriately rounds off large numbers.
• Puts numbers into perspective.

6
A map should be clear and uncluttered
(Unlike this one.)
7
Does this work?
Map is cluttered, but Purpose here is to
locate, not to present data.
8

• Would numbers and a legend (as done here) be more
  clear?

9
Accounting for inflation
Stamp prices shown are misleading
10
Accounting for inflation
unless you consider the changing value of the
dollar, as indicated by the lengthened lines.
Check inflation at bls.gov
11
Accounting for inflation
Heres an interesting chart showing the growth of
the Maine lobster business. The problem is
12
Accounting for inflation
Value of lobsters in 2000 dollars
It doesnt reflect the change in the value of
the dollar
13
Accounting for inflation
6.00
Price Per Pound in 2000 dollars
3.00
Actually, the price peaked in 1973!
1950
2002
14
Accounting for inflation
15
Linear deception
16
Linear deception
Is the footnote enough here? Shouldnt we do
something else to show readers that the 04
figures are for part of a year?
17
Here, change is clearly labeled

• But should we graph such a tentative number?

18
Linear deception?
Does something look wrong here?
19
Linear deception?
Why are injuries rising and deaths falling?

1. Deaths are reported deaths accident figures are
   estimates, based on a survey of 100 emergency
   rooms.
2. CPSC estimates actual deaths at figures higher
   than the reported deaths. Should chart use those
   numbers?
3. Should we include the 2004 figures at all?

20
Controlling for population
The chart shows differences in funding amounts
among states and some cities, but those
differences mainly reflect population
differences. Compare it with a graph of the state
populations.
21
Controlling for population
A per-capita comparison presents a very different
picture.
22
Be wary of pie charts

• They do a poor job in ranking proportions.
• The numbers and the slices can be hard to
  connect.
• The slices get to be too thin for nourishment.

23
What to do instead?

• Often, simple tables are best.
• Consider the cake chart.

• Shares are more clear.
• Rank ordering is simpler.

But What about the number of accidents?
24
Car safety experts shift focus to side impact As
highway deaths have declined, the share of deaths
blamed on side impact crashes has risen.
A lot more information in the same space.
Front Impact Other Side Impact
86 (52)
62 (53)
Car fatalities, by direction of impact
1980-2001 Driver deaths in cars 1-3 years old,
per million cars registered
41 (46)
36 (22)
18(15)
14(17)
42 (26)
37 (32)
32 (37)
25
A Clear Comparison
But can the graph show more?
26
Accounting for the change in population
27
Worth the space? (Few data points)
28
Worth the space? Doesnt a table work as well?
29
Worth the space? Where a chart works well
30
A neat graphic
Lots of data in a limited space
31
Mistakes of magnitude
32
True confessions
Errors that made our papers
33
More true confessions
34
More true confessions
35
True confessions, contd,
36
Great catches
37
Great catches
38
Great catches
39
Great catches