Editing graphics July 10, 2006 Bill Cloud University of North Carolina at Chapel Hill

Editing graphics

July 10, 2006Bill Cloud

University of North Carolina at Chapel Hill

The agenda

• Game 1: Find the error.

• A quick look at graphics.

• Discussion: How can we reduce errors?

• Game 2: What’s my question?

A good map or chart: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.

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.

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.

A map should be clear

and uncluttered

(Unlike this one.)

Does this work?Map is cluttered,

but:

•Purpose here is to locate, not to present data.

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

Accounting for inflation

Stamp prices shown are misleading …

Accounting for inflation

…unless you consider the

changing value of the dollar, as

indicated by the

lengthened lines.

Check inflation at bls.gov

Accounting for inflation

Here’s an interesting chart

showing the growth of the Maine lobster business. The problem is …

Accounting for inflation

Value of lobsters in 2000 dollars

… It doesn’t reflect the change in the value of the dollar

Accounting for inflation

Price Per Pound in 2000 dollars

Actually, the price peaked in 1973!

1950 2002

6.00

$3.00

Accounting for inflation

$60.29 in 2006 dollars.

Linear deception

Linear deception

Is the footnote enough here? Shouldn’t we do something else to show readers that

the ’04 figures are for part of

a year?

Here, change is clearly labeled

• But should we graph such a tentative number?

Linear deception?Does something look

wrong here?

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?

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.

Controlling for population

A per-capita comparison presents a very different picture.

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.

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?

0

20

40

60

80

100

120

140

160

180

1980-81 1990-91 2000-01

Car fatalities, by direction of impact – 1980-2001

Driver deaths in cars 1-3 years old, per million cars

registered

86 (52%)

62 (53%) 41

(46%)

42 (26%)

37 (32%)

32 (37%)

36 (22%)

18(15%)14(17%)

Front Impact

Other

Side Impact

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.

A Clear ComparisonBut

can the graph show more?

Accounting for the change in population

Worth the space?

(Few data points)

Worth the space?Doesn’t a table work as well?

Worth the space?Where a chart works well

A neat graphic

Lots of data in a limited space

Mistakes of magnitude

True confessions: Errors that made our papers

More true confessions

More true confessions

True confessions, cont’d,

Great catches

Great catches

Great catches

Great catches