Post on 13-Nov-2014
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Chapter 2 and Infographics Project
Graphs: Good, Bad & Ugly
A visual presentation of dataRelationships & comparisons are visual Less daunting to some than tables of numbersAllows some artistry and creativity
Accuracy is importantStyle of graph must match
Scale (level) of measurement of the variable(s)Nature of this particular data set
Purpose of a Graph
Axes drawn and labeledCategory values labeledTitle for graphData bars proportional to number of cases in dataBalancedMaintains scaleNo “chart junk” Not complicatedOnly one idea conveyed
Graph that meets basic requirements
Data are in categoriesNominal Ordinal (if few categories)
Types of graph:Pie ChartBar Chart or Pictograph (Excel: Column chart)
Show the Frequency (count) or Percent
Graphs for Discrete Data (counts)
Area of bars combined is 100%
Area of each bar is proportional to its percent of total
Bars do not touchbecause categoriesare discrete.
Many variations; this is the most simple.
BAR CHART: the Good
The Bad:design hides trends or data
PICTOGRAPH: the Good bars constructed of equal size simple icons
PICTOGRAPH: the Ugly
Elements of unequal size
Just heads of some kids
All children are playing except those from China – subtle racism
BAR CHART – problems to consider:area, color – & why is that jogger there?
Practice: How many problems can you see in this graph?
Area of pie = 100%Wedge is proportional to percentage of casesLabels show count or percent Ten slices is the maximum to remain clear & readable.
PIE CHART: the Acceptable
PIE CHART: the Badcharts confuse or obscure the pattern in the data
What can you detect in this old graph?
Graph shows continuity of the constructHistogram: bars that touch at real limitsLine graph: covers range
(a.k.a. Frequency Polygon)Horizontal axis goes from low to high
Intervals shown for Interval or Ratio dataSome ordinal data also graphed this way
(e.g., strongly agree, agree, slightly agree, etc)
Graphs for Continuous Data (sometimes used for Ordinal data)
Bar width is a rangeof scores or the reallimits of scores.
Ranges equal widthLabels show mid-
point or real limitsLow scores on left,
high scores on right
HISTOGRAM: the Good
HISTOGRAM: the BadRanges of data
Unequal & indeterminateSpacing of “bars” is unequal.Water, sky, umbrella detract from graph
Curved horizontal axis so no vertical axis.Lowest categories are on the right, not left.Intervals of income are unequal/indeterminate.One interval is just plain wrong, and data are lost (all incomes $49,001 to $49,999 omitted).
HISTOGRAM:the Ugly
Same requirements as histogram.
If more than one line,legend or labels are needed.
More than four or fivelines can be hard tointerpret
Line Graphs / Frequency Polygon
from SRB Documentary. (2008). Demographic Winter: the Decline of the Human Family at http://www.demographicwinter.com/index.html
LINE GRAPH: the Bad
Why is the headline “Steady growth” for this graph?Hint: check the axis values
If it is growth, is it steady ?Hint: how did each of the
three variables change from 1988 to 1989.
Modern graphs have more options
The Future of Food. (2008) Wired Magazine 16:11
Chapter 2 and Infographics Project
Graphs: Good, Bad & Ugly