MATH 141 Lecture Notes - Lecture 4: Interquartile Range, Quartile, Percentile
15 Sep 2016
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Suppose the observations are already arranged in ascending order, then the p-th percentile is the value such that p% of values fall below it: ex. A rough but simple way to find pth percentile =-th number in the list. This approach is not accurate, thus cannot be used to find medial and quartiles. Quartile: lower quartile (ql=q1): a number that 25% observed values are less than it, and another. 75% are greater than it: upper quartile (qu=q3): a number that 75% of observed values are less than it, and another 25% are greater than it. *fences used to detect unusual values / outliers: q1 - 1. 5 x iqr, q3 + 1. 5 x iqr. Fences used to detect far-outliers: q1 - 3 x iqr, q3 + 3 x iqr. Z-score is the number of standard deviations of a value from the average: za =
