Measures of Spread

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Measures of Spread
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• Spread, dispersion and variation all refer to a
  measure of the way a data set is distributed
  around a central value.

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Ways to Measure Spread

• 1. Range the difference between the max and min
  values.
• Quartiles The 3 median values that divide the
  data into 4 equal parts.
• Interquartile Range the difference between the
  first and third quartiles. Contains the middle
  50 of the data.

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• 4. Variance measure of dispersion that is found
  by averaging the squares of the deviation
  (distance from the mean) of each piece of data
• Calculating Variance

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• Standard Deviation the square root of the
  variance
• Calculation

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What do these measures tell us about the data?

• Quartiles and Interquartile Range
• tell us how spread out the middle 50 of the data
  is
• Helps in constructing a box plot
• Variance
• how the elements are spread around the mean.
• large variance means the data is widely spread
  around the mean.

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• Standard Deviation
• The standard deviation is in the same 'scale' as
  the mean is. The makes these two indicators
  'comparable'.
• how the elements are spread around the mean.
• large variance means the data is widely spread
  around the mean.