A z-score is the number of standard deviations that a given value x is above or below the mean.
z-scores have no units of measurement
A data value is significantly low if its z-score is less than or equal to -2, or significantly high if the z-score is greater than or equal to 2
Percentiles are 1 type of quantiles, or fractiles, which partition data into groups with roughly the same number of values in each group.
Percentiles are measures of location, which divide a set of data in 100 groups with about 1% of the values in each group
Percentile of value x = ( (number of values < x) / total # of values ) * 100
Quartiles are measures of location, denoted Q1, Q2, Q3, which divide a set of data into 4 groups with about 25% of the values in each group
5 number summary consists of: minimum, Q1, Q2 (or the median), Q3, maximum
A boxplot is a graph of a data set that consists of a line extending from the minimum value to the maximum value, and a box with lines drawn at the first quartile, the median, and the third quartile.
A modified boxplot is a regular boxplot constructed with these modifications:
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