Box and Whisker Plots
Understanding and using Box and Whisker Plots (Box Plots)
How to read Box and Whisker Plots
Box and whisker plots portray the distribution of your data, outliers, and the median. The box within the chart displays where around 50 percent of the data points fall. It summarizes a data set in five marks. The mark with the greatest value is called the maximum. It will likely fall far outside the box. The mark with the lowest value is called the minimum. It will likely fall outside the box on the opposite side as the maximum.
The box itself contains the lower quartile, the upper quartile, and the median in the center. The median is the value separating the higher half from the lower half of a data sample, a population, or a probability distribution. You can think of the median as "the middle" value in a set of numbers based on a count of your values rather than the middle based on numeric value. These sections help the viewer see where the median falls within the distribution. The lower quartile is the 25th percentile, while the upper quartile is the 75th percentile. The median is the middle, but it helps give a better sense of what to expect from these measurements. The whiskers (the lines extending from the box on both sides) typically extend to 1.5* the Interquartile Range (the box) to set a boundary beyond which would be considered outliers. Hence the name, box, and whisker plot.