Activity
1. Start class with a quick
review of yesterday’s lesson: Yesterday you
were reading and interpreting graphs to get information to
answer some questions. Being able to read a graph is similar
to reading a book, it gives you power to make your own decisions.
Unfortunately, just as some books give you slanted opinions
or information that could best be described as propaganda,
some graphs present distorted data in the hope of getting
you to reach the same decision as the person who made the
graph. If you know what to look for--and look out for--graphs
can be very useful to you. If you are not careful, though,
they can be very manipulative. Graphs must be viewed carefully
for the following reasons:
• Graphs
have more impact than tables or "raw" data
because graphs are visual. They can bypass the analytic
part of your brain unless you take care to look closely.
• Graphs represent interpretations of data. When the data has been specially
selected, then the graph represents an interpretation of selected data.
• A given set of data can be plotted to create almost any impression. Because
of the techniques available for constructing a graph, a graph may show a dramatic
trend upward or downward when in fact the data do not support such an apparent
change.
• The person who draws the graphs influences the impact of the information
and thus influences the decision to be made from the graphs.
Source: http://www.virtualsalt.com/think/vislit1.htm
2.
A list of common distortions the students might see in
graphs follows. Discuss each case with students.
• False
perspective. (Put up the Avoid 3-D overhead to demonstrate
False Perspective)
o
Tilting a pie chart
o Making 3-D representations of data that is better represented in
2-D
• Leaving
out important data. (Put up the Traffic Fatalities
Overhead to demonstrate how leaving out the earlier
years makes a stronger case for enforcing stricter
motorist laws in order to reduce the number of fatalities.)
• Adding extraneous data. (Put up the World On Line Overhead to demonstrate
how shifting the horizontal axis to February made WOL look better, i.e. not showing
such a sudden drop, even though there was no stock market quotation for WOL until
March)
• Using different horizontal scale units. (Put up the Incomes of Doctors
Overhead to demonstrate how using different horizontal scale units change the
presentation of data.)
• Not putting in scales on either axis or combining two graphs, which have
different scales, into one graph. (Put up the Most Misleading Graph Overhead
to demonstrate this)
• Inconsistent scales/different starting points for the scale. (Put up
the Inconsistent Scales Overhead to demonstrate this.)
The
list of has been adapted from: http://www.sociology.ohio-state.edu/classes/soc549/vonhippel/
3.
Either in class or for homework, have the students create
two different graphs for each set of data: one that exaggerates
the difference (smaller value per vertical unit) and
another that does not exaggerate the difference (larger
value per vertical unit)
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