# STATS 250 Lecture Notes - Lecture 4: Unimodality, French Fries, Standard Deviation

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15 Sep 2016
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## Document Summary

Bell-shaped somewhat symmetric unimodal representation of data. Standard deviation roughly the average distance the observations fall from the mean: actually the square root of the squared deviation of observations from the mean s = sample standard deviation = = S2 = variance: emphasize the standard deviation because it is in the original units. Ex: the weights of small orders of french fries are roughly 6. 1 g away from their mean weight of 73. 5g. S=0 means that there is no variability or spread; all observations have the same value. Like the mean, s is very sensitive to outliers or extreme observations. Whenever you use the mean as the measure of center, use standard deviation as a measure of spread. Use the mean and standard deviation for symmetric bell-shaped distributions. Five-number summary is better for skewed distributions or outliers. Statistic numerical summary based on a sample: sample mean, sample standard deviation.

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