STATS 250 Lecture Notes - Lecture 3: Interquartile Range, Quartile, Box Plot

• School: U of M
• Department: Statistics
• Course: STATS 250
• Professor: Alicia Romero

Document Summary

When an average is reported, a measure of spread or variability is necessary to gauge the meaning. Range measures the spread over 100% of the data: range = high value low value = maximum minimum. Percentiles the pth percentile is the value such that p% of the observations fall at or below that value. Common percentiles: median (m) = 50th percentile, first quartile (q1) = 25th percentile = median of all the values below the median, third quartile (q3) = 75th percentile = median of all the values above the median. A quick way to provide an overview of the center and spread of the data is by dividing the data into approximate quarters with the five number summary. Interquartile range (iqr) measures the spread over the middle 50% of the data: iqr = q3 q1. Boxplots a graphical representation of the five number summary.