2.3 Measures of Dispersion


-Which Airplane Would You Use?


Two measures of dispersion:

  1. standard deviation
  2. z-score



Def: Standard Deviation: the average distance from the mean.



Def: z-score: indicates how many standard deviations above or below the mean your score lies.



Empirical Rule:   68% of scores are within 1 standard deviation from the mean

                             95% of scores are within 2 standard deviations from the mean, and

                             99% of scores are within 3 standard deviations from the mean














Formula for computing z-score by hand: