Data Lab

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Data Lab 2Descriptive StatisticsMay 28, 2008

• Ivan Katchanovski, Ph.D.
• POL 242Y-Y

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Measures of Central Tendency The Mode

• The mode is the only measure of central tendency
  for nominal variables
• The mode can also be found for ordinal and
  interval-ratio variables
• Example select a nominal variable
• colony (World dataset)
• SPSS Command
• Analyze-Descriptive Statistics-Frequencies-Statist
  ics-Mode
• Identify the mode by a value in statistics box
• Identify the mode by a value with the highest
  frequency
• Identify the mode by a value with the highest
  percentage in valid percent column

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Measures of Central Tendency The Median

• The median is appropriate for ordinal and
  interval-ratio variables
• The median is not appropriate for nominal
  variables
• Example Select an ordinal variable
• Economic development (World dataset)
• SPSS Command
• Analyze-Descriptive Statistics-Frequencies-Median
• Identify the median by a value in statistics box
• Identify the median by a value below which 50
  of cases lie in cumulative percent column

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Measures of Central Tendency The Mean

• The mean is only appropriate for interval-ratio
  variables
• Example Select interval ratio variable
• GDP per capita 1000 (World dataset)
• SPSS Command
• Analyze-Descriptive Statistics-Frequencies-Statist
  ics-Mean
• Identify the mean by a value in statistics box

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Graphic Description of Variables Bar Chart

• Bar chart
• Most appropriate for nominal and ordinal
  variables
• Shows dispersion of a variable
• Example select a nominal variable
• colony (World dataset)
• SPSS Commands
• Analyze-Descriptive Statistics-Frequencies-Charts-
  Bar charts-Percentages
• Open Chart Editor Select chart-Edit-SPSS Chart
  Object-Open
• In Chart Editor Options-Title
• In Chart Editor Elements-Show Data Labels

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Graphic Description of Variables Pie Chart

• Pie chart
• Most appropriate for nominal and ordinal
  variables with small number of values
  (categories)
• Example select an ordinal variable
• economic development (World dataset)
• SPSS Commands
• Analyze-Descriptive Statistics-Frequencies-Charts-
  Pie charts-Percentages
• Open Chart Editor Select chart-Edit-SPSS Chart
  Object-Open
• In Chart Editor Options-Title
• In Chart Editor Elements-Show Data Labels

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Graphic Description of Variables Histogram

• Histogram
• Most appropriate for interval-ratio variables
  with large number of values
• Shows dispersion of a variable
• Example select an interval-ratio variable
• GDP per capita 1000 (World dataset)
• SPSS Commands
• Analyze-Descriptive Statistics-Frequencies-Charts-
  Histograms
• Open Chart Editor Select chart-Edit-SPSS Chart
  Object-Open
• In Chart Editor Options-Title
• In Chart Editor Elements-Show Data Labels

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Skewness of Distributions

• Skewness of distributions
• Appropriate for interval-ratio variables
• Example select an interval-ratio variable
• GDP per capita 1000 (World dataset)
• SPSS Commands
• Analyze-Descriptive Statistics-Frequencies-Statist
  ics-Skewness/Mean/Median
• Unskewed distribution if skewness statistics0 or
  meanmedian
• Positively skewed distribution if skewness
  statisticsgt0 or meangtmedian
• Negatively skewed distribution if skewness
  statisticslt0 or meanltmedian

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Helpful SPSS Options

• SPSS option for displaying variable labels
  instead of variable names
• Open the 2000 World Values Survey Dataset
• Edit-Options-General-Display labels
• SPSS option for selecting cases
• Example selecting Canadian respondents from the
  World Values Survey dataset
• Identify value for Canada (12) in nation
  variable (v2)
• Data-Select cases-If v212

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Dependent and independent variables

• Describing dependent and independent variables
• The 2000 World Values Survey
• Questionnaires
• Country specific questionnaires online at
  http//www.worldvaluessurvey.org/
• Documentation of the Values Surveys
  1999-2004 wave
• Select Canadian questionnaire and Canadian sample
  of the 2000 World Values Survey dataset
• Identify dependent variable
• Identify independent variable
• Produce appropriate descriptive statistics and
  charts