Descriptive Statistics

1
Descriptive Statistics

• Measure of central tendency
• Gives a typical value for the data set
• Tells you where the middle of the data set is
• Measure of dispersion
• Indicates how the data are spread out
• Tells you what the rest of the data are doing

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2
Descriptive Statistics

• The aim of descriptive statistics is to give an
  accurate summary of the data
• The wrong choice of statistic gives a distorted
  picture of the data
• This can lead to the wrong conclusions being
  drawn from the data
• Each measure of CT and D has its advantages and
  disadvantages

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3
Measures of Central Tendency

• The mean
• Adv it uses all the values in the set, so is
  most sensitive to variations in the data
• Dis it can be artificially raised or lowered by
  an extreme value, or by skewed data
• Use it when the data are normally distributed,
  unskewed and there are no outliers

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4
Measures of Central Tendency

• The median
• Adv it is based on the order of the data, not
  their actual values, so not distorted by extreme
  values
• Dis however, this makes it less sensitive to
  variations in the data
• Use it when you cant use the mean because of
  skew, outliers etc.

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5
Measures of Central Tendency

• The mode
• Adv its the only measure suitable for
  summarising category/frequency data
• Dis for many data sets there is no modal value,
  or their may be several
• Use when dealing with frequency data, and/or
  where there is a clear modal value in the set

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