Exploring, Describing, Displaying and Summarizing Data

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Exploring, Describing, Displaying and Summarizing
Data

• January 31, 2005

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General Philosophy

• Tables and graphs are an efficient way for the
  researcher to present a large amount of data in a
  small amount of space.
• Tables and graphs are effective only when the
  data are arranged so that their meaning is
  obvious at a glance (Ehrenberg, 1977)

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Tables Graphs

• Visual representations of the data
• If used appropriately, can be an effective way to
  summarize and communicate information
• If used inappropriately, can be very confusing
  and distracting.

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• What the statistician often needs -- is enough
  different "looks" to have a good chance to learn
  about this real world.

Tukey, 1964
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Matching variables to graphs that represent the
raw data values
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HISTOGRAMS

• X-axis
• Contains category names
• Y-axis
• Contains count or frequency or percent
• Best to create Histograms in EXCEL
• Can be created in SPSS, but SPSS graphs are
  difficult to customize and get into APA format

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Data used BP.SAV
Histograms
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Example of a Really Bad Histogram
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Data used BP.SAV
Pie Charts
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Example of a Really Bad Pie Chart
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General Rules for Histograms and Pie Charts

• Histograms
• No more than 15-20 categories
• Can be vertical or horizontal
• If variable is nominal, you should order your
  categories from low to high or high to low
• Pie Charts
• No more than 3-6 categories
• Choose colors carefully most publications will
  print chart into black white

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Assignment for next class

• Create a histogram and a pie chart that
  summarizes the variable Race in the BP.SAV
  dataset. Copy and paste this graph into a Word
  document.
• Download the SUICIDE.SAV file and try to make the
  various histograms and pie charts that I have
  shown here.

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FYI Cartesian Coordinates System

• Cartesian coordinates system for representing the
  relative positions of points in a plane or in
  space. In a plane, the point P is specified by
  the pair of numbers (x, y) representing the
  distances of the point from two intersecting
  straight lines, referred to as the x-axis and the
  y-axis. The point of intersection of these axes,
  which are called the coordinate axes, is known as
  the origin. If the axes are perpendicular, as is
  commonly the case, the coordinate system is
  called rectangular otherwise it is oblique. In
  either type the x-coordinate, or abscissa, of P
  is measured along a line parallel to the x-axis,
  and the y-coordinate, or ordinate, along a line
  parallel to the y-axis. A point in space may be
  similarly specified by the triple of numbers (x,
  y, z) representing the distances from three
  planes determined by three intersecting straight
  lines not all in the same plane. Named for the
  French philosopher and scientist René DESCARTES.
• From encyclopedia.com

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René Descartes

• He entered the college at the age of eight years.
• While in the school his health was poor and he
  was granted permission to remain in bed until 11
  o'clock in the morning.
• The only subject which was satisfactory in his
  eyes was mathematics.
• Only mathematics, Descartes feels, is certain, so
  all must be based on mathematics.
• In 1649 Queen Christina of Sweden persuaded
  Descartes to go to Stockholm. However the Queen
  wanted to draw tangents at 5 a.m. and Descartes
  broke the habit of his lifetime of getting up at
  11 o'clock. After only a few months in the cold
  northern climate, walking to the palace for 5
  o'clock every morning, he died of pneumonia.
• http//www-groups.dcs.st-and.ac.uk/history/Mathem
  aticians/Descartes.html