Standard Deviation

Deviation: how far a score is from the mean. deviation = score - mean

Mean Deviation: the average of all the deviations

Standard Deviation: The square root of the mean of the sum of the squares of all the deviations.

Standard deviation is NOT Mean Deviation

Population vs Sample

Population

$o=\sqrt{\frac{\sum (x-\mu {)}^2}{n}}$ $\mu$ is the mean of the population

Sample

n-1 is the more accurate for samples, thats why its n-1 this time s = $\sqrt{\frac{\sum (x-\overline{x}{)}^2}{n-1}}$ $\overline{x}$ is the mean of the sample

Z-Score

z-score: the number standard deviation a score is from the mean.

Population

z = $\frac{x-\mu }{\sigma }$

Sample

z = $\frac{x-\overline{x}}{s}$

There is a formula, but there is also a way to do it on ur calculator Standard Deviation Mode`