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Chapter 4: Variability - Coggle Diagram

- - - - Not used often, typically unreliable/unhelpful as a measure of variability
    - - Quartiles are represented by their upper real limits
      - Helps to eliminate outliers
      - Used alongside the median (the 2nd quartile)
      - Can be used on ordinal scales
  - - - However, when calculating sample standard deviation and variance, use the number of values minus 1 (n-1) instead of the number of values (n) to correct against bias.
        
        After dividing by n-1 instead of n, the statistic can now be said to be unbiased
        
        Unbiased Statistic: A statistic where the average value of the statistic is equal to the population parameter.
    - - Computational formula: Sum of squared values minus (the square of the sum of values over the number of values)
        
        Avoids having to calculate deviations, which can be annoying to square
        
        These are the same for population and sample.
      - Definitional Formula: Sum of the (values minus mean) squared.
        
        Most direct representation of how the sum of squares is found
    - - Biased Statistic: A statistic where the average value of the statistic is unequal (either under or over) the population parameter
        
        Correct for bias