2.3 Measures of Dispersion

-Which Airplane Would You Use?

Two measures of dispersion:

- standard deviation
- 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: _{}