Organizing and Presenting Data

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Organizing and Presenting Data

• GTECH 201
• Session 11

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Terminology

• Classes
• Categories for grouping data
• Frequency
• Number of observations that fall in a class
  (frequency is a count)
• Frequency Distribution
• A listing of all classes along with their
  frequencies
• Relative Frequency
• The ratio of the frequency of a class to the
  total number of observations
• Relative Frequency Distribution
• A listing of all classes along with their
  relative frequencies
• Width/Class Interval
• The difference between the upper and lower cut
  points (breaks) of a class

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Organizing Data

• Classification Rules
• Aim is to create categories or classes
• First step is to compute range
• Range Largest Value Smallest Value
• Interval or Ratio Scale data only
• Class Intervals
• Width of Class Interval
• Equal based on range
• Unequal based on range
• Quantile (Quartile or Quintile)
• Natural

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Classification Methods

• Natural breaks

• Quantile

• Manual

• Equal interval

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How to Decide(on a classification scheme)

• Rule of thumb 3 - 7 classes
• Classification histogram (see later today)

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How to Decide, part II
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Graphs

• Line graph
• Bar graph
• Scatterplots

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Creating a Line Graph

• The growth of the population of students at a
  Midwestern university is as follows

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Line Graph
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Bar Graphs

• Here are data on the percent of females among
  people earning doctoral degrees in 1990, in
  several different fields of study

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Bar Graph
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Scatter Plots

• Graph bi-variate data when both variables are
  measured in an interval/ratio or ordinal scale
• Units for one variable are marked on the
  horizontal axis
• Independent variable should always go on the
  horizontal, x axis

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Scatterplots

• Survey of 3368 people asking them to estimate
  number of calories in common foods.

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Example

• A city planner collected data on the number of
  school age children in each of 30 families.
• Construct a grouped data table using classes
  based on a single value

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Computing Frequency

• There are three ways you can create classes
• a lt but not equal to b
• b lt but not equal to c
• a b, c d, e - f
• single value grouping

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Distributions

• Histograms
• Difference between histograms and bar graphs
• Bars in a histogram are always vertical
• Base scale is marked off in equal units there
  is no base scale in a bar graph
• Width of bars in a histogram have meaning
• Bars in a histogram touch each other

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Constructing a Histogram

• Histogram height of bar equal to frequency of
  class represented
• Bar extends from lowest value to highest value of
  the class

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Histogram Chart
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Frequency Polygons

• Similar to a histogram
• Midpoint of the class is indicated
• Points connected by straight lines
• Cumulative frequency polygon, ogive

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