Lathe 3 is performing with relatively less variation than Lathe 2 however, it is centered on the lower side of the specification and is making shafts below specification.| Ian Baldwin How to do Box Plot Calculations in Tableauīox plots are great for displaying distribution and in Tableau they’re incredibly easy to make.Lathe 2 appears to have excess variation, and is making shafts below the minimum diameter.Lathe 1 appears to be making good parts, and is centered in the tolerance.The design specification is 18.85 +/- 0.1 mm.ĭiameter measurements from a sample of shafts taken from each roughing lathe are displayed in a box and whisker plot in Figure 2.įigure 2 Box and Whisker Plot Lathe Comparison Example Suppose you wanted to compare the performance of three lathes responsible for the rough turning of a motor shaft. Right figure: For comparison, a histogram of the data is also shown, showing the frequency of each value in the data set. The median value is displayed inside the "box." The maximum and minimum values are displayed with vertical lines ("whiskers") connecting the points to the center box. Left figure: The center represents the middle 50%, or 50th percentile of the data set, and is derived using the lower and upper quartile values. The data represented in box and whisker plot format can be seen in Figure 1. Note: For a data set with an even number of values, the median is calculated as the average of the two middle values.
Maximum value: The largest value in the data setįor example, given the following 20 data points, the five required statistics are displayed.Third quartile: The value above which the upper 25% of the data are contained.Median value: The middle number in a range of numbers.Second quartile: The value below which the lower 25% of the data are contained.Minimum value: The smallest value in the data set.
You can also download the box and whisker plot template. The procedure to develop a box and whisker plot comes from the five statistics below.
Quality Glossary Definition: Box and whisker plotĪlso called: box plot, box and whisker diagram, box and whisker plot with outliersĪ box and whisker plot is defined as a graphical method of displaying variation in a set of data.