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