LIS 504 - Graphic displays of data

Much of this information is derived from

What graphic displays should do

Graphical integrity

Lie factor

lie factor = size of effect shown in graph
size of effect in data
where
size of effect = |second value - first value|
first value
A lie factor that is either much higher or much lower than one is bad. A high lie factor exaggerates differences between values. A low lie factor obscures differences between values.

A common example of a high lie factor occurs when both dimensions of a two-dimensional figure are made proportional to the same data, so that the size of the figure is proportional to the square of the data; for instance,
Year Books circulated
2001 100 &
2002 141 &
2003 200 &
where the lie factor is about 2.4.

An example of a low lie factor can be seen in the "Cones" custom chart format in Microsoft Excel.

The heights of the (truncated) cones are proportional to the data, but their areas on the screen and their apparent volumes make the larger data values seem relatively small.

Charting on a logarithmic scale can also produce a low lie factor.

Data-ink ratio

data-ink ratio = "ink" used to display the data            
total "ink" used to display the graphic
The data-ink ratio should be relatively high.

A low data-ink ratio can be a result of "chartjunk". Types of chartjunk include

Data density

data density = number of entries in data matrix
area of data graphic
The data density should be relatively high.

If there are not enough data points to support a high data density in a graphic, using a simple table may be a better idea.


Home

Last updated November 6, 2000.
This page maintained by Prof. Tim Craven
E-mail (text/plain only): t.craven@uwo.ca
Faculty of Information and Media Studies
University of Western Ontario,
London, Ontario
Canada, N6A 5B7