Graphs, Good and Bad

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Graphs, Good and Bad
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Two types of variables

• Categorical variables- places individuals into
  one of categories or groups
• Examples gender, ethnic groups, model of car,
  etc
• Quantitative Variables take numerical values
  for which arithmetic operations such as adding
  and averaging make sense.
• Examples Age, weight, income etc.

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Starting with a Table

• Note- Very important title
• The Number of Kids per household of parents 25-35
  years old

Number of households Percent
0 children 8481 15.6
1 child 17071 31.4
2 children 23268 42.8
3 children 4621 8.5
4 plus children 924 1.7
Total 54365 100
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Graphs used to organize data

• Pie charts used when looking at a fraction of a
  whole equals 100- qualitative or categorical
  data
• Bar Graphs- used when data points are few. Used
  with qualitative data /DV-numerical/IV
  non-numerical
• Line Graph- used when you have 2-3 variables,
  experimental results-quantitative data /IV and DV
  are both numerical

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Pie Charts use when working with percents

• Used for Categorical or qualitative Variables
  looking at a fraction of a whole
• To make a pie chart, first draw a circle. The
  circle represent a whole. Wedges within the
  circle represent the parts. The angle spanned by
  each wedge is in proportion to the size of that
  part.
• For instance, If we were displaying the amount of
  education people have had and 21.3 had a
  bachelors degree we would make that slice 77?
  wide.
• 0.213 ? 360? 77?

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Example Pie chart
Pie Chart showing the number of children found
per household
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Bar Graphs

• Use for Categorical or qualitative Variables
• The height of the bars show the percent of each
  category
• The width of the bars need to be the same

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Example - Bar Graphs
Bar Graph- showing number of children per
household
Number of houses
Number of children
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• Pie chart
• Only compare parts of a whole
• are often hard to read since it is difficult to
  compare the angles of the different pieces of the
  pie
• Bar graphs
• can compare quantities that are not parts of a
  whole
• Easier to interpret than a pie chart

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Line Graph- shows trends, dramatic changes or
patterns

• A line graph is used for graphing quantitative
  variables that change over time
• Ex bank account over time, water levels over
  time, and performance of stocks
• Put time (IV) on the horizontal scale( x axis)
  and the variable you are measuring (DV) on the
  vertical scale
• ( y axis)
• Use with many data points, May have more than 1
  variable (line)
• Connect the data points by lines to display the
  change over time

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Example - Line Graph
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Making good graphs

• Label the x and y axes
• Tell which units you used for your variables
• X axis is independent variable/ Y axis is
  dependent variable
• Title of Graph dependent variable vs
  independent variable