Compare the interquartile ranges that is, the box lengths , to examine how the data is dispersed between each sample. The longer the box the more dispersed the data. The smaller the less dispersed the data. Next, look at the overall spread as shown by the extreme values at the end of two whiskers. This shows the range of scores another type of dispersion. Larger ranges indicate wider distribution, that is, more scattered data.
If the data do not appear to be symmetric, does each sample show the same kind of asymmetry? McLeod, S. What does a box plot tell you? Toggle navigation. Statistics Box and Whisker Plot What does a box plot tell you? By Saul McLeod , published What is a box plot? Box plots are useful as they show the average score of a data set. Box plots are useful as they show the skewness of a data set. The box plot shape will show if a statistical data set is normally distributed or skewed.
There are two potential outliers in distribution A. Please contact us and let us know how we can help you. Table of contents. Topic navigation. Figure 4. Description for Figure 4. In a box and whisker plot: The left and right sides of the box are the lower and upper quartiles. The vertical line that split the box in two is the median. Sometimes, the mean is also indicated by a dot or a cross on the box plot. Note: For a data set with an even number of values, the median is calculated as the average of the two middle values.
Figure 1 Box and Whisker Plot Example. The median value is displayed inside the "box. Right figure: For comparison, a histogram of the data is also shown, showing the frequency of each value in the data set. Suppose you wanted to compare the performance of three lathes responsible for the rough turning of a motor shaft. The design specification is Diameter measurements from a sample of shafts taken from each roughing lathe are displayed in a box and whisker plot in Figure 2.
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