Frequency Distributions

• A frequency distribution allows us to begin to organize the data.
• Data is divided into a number of classes
• Each of these classes has the same width
• The classes do not overlap
• Each piece of data belongs to exactly one class.
• A class is characterized by the lower class limit and the upper class limit
• Relationship between class limits and class width.
  • The class width = the difference between the lower class limit of two adjacent classes
  • The class width = the difference between the upper class limit of two adjacent classes
  • The class width = the difference between the upper class limit and the lower class limit +1 of a single class.
• The midpoint of a class or the class mark is found by (lower class limit + upper class limit) / 2
• The modal class is the class with the greatest frequency.
• Do problems 9, 11 page 848

Statistical Graphs

• Circle graphs or pie charts are a quick way to display data.
• Find percentages associated with each class.
• Each angle is percentage * 360
• A histogram or bar chart will also allow a summary of the data.
• Make sure to label with class mark.
• A Frequency polygon displays the same data, but with a line.
• A stem and leaf display is a poor man's histogram.

  10 15 24 36 48 45
  42 53 60 17 24 30
  33 45 48 62 54 60
  
      1|5 represents 15
  Stem | Leaves
      1| 0 5 7
      2| 4 4
      3| 6 0 3
      4| 8 5 2 5 8
      5| 3 4
      6| 0 2 0