STAT-2300 Lecture Notes - Lecture 5: Quartile, Percentile
3 Mar 2017
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Document Summary
Another measure of position for an observation is its percentile. Determining and understanding percentiles is usually done better visually than by reading the definition, but a percentile is determined based on what percent of observations is to the left of it. For any set of # observations arranged in order, the pth percentile is a number such that. P% of the observations fall below the pth percentile, and 100-p% of observations fall above it. Given this, a percentile acts almost like an observation cap, where the number of the percentile is the maximum number of observations than can be below it. Quartiles are a very common kind of percentiles, however instead of being able to separate the data at whatever point is chosen, quartiles split the data up in to four equal parts. The first quartile, q1, represents the 25th percentile, or the first 25% of data. The second quartile is just the median, which represents the 50th percentile.
