Median ( Q 2 or 50th percentile): the middle value in the data set.Maximum ( Q 4 or 100th percentile): the highest data point in the data set excluding any outliers.Minimum ( Q 0 or 0th percentile): the lowest data point in the data set excluding any outliers.Same box-plot with whiskers drawn within the 1.5 IQR valueĪ boxplot is a standardized way of displaying the dataset based on the five-number summary: the minimum, the maximum, the sample median, and the first and third quartiles. Box plots can be drawn either horizontally or vertically.įigure 3. In addition, the box-plot allows one to visually estimate various L-estimators, notably the interquartile range, midhinge, range, mid-range, and trimean. The spacings in each subsection of the box-plot indicate the degree of dispersion (spread) and skewness of the data, which are usually described using the five-number summary. Outliers that differ significantly from the rest of the dataset may be plotted as individual points beyond the whiskers on the box-plot.īox plots are non-parametric: they display variation in samples of a statistical population without making any assumptions of the underlying statistical distribution (though Tukey's boxplot assumes symmetry for the whiskers and normality for their length). In addition to the box on a box plot, there can be lines (which are called whiskers) extending from the box indicating variability outside the upper and lower quartiles, thus, the plot is also termed as the box-and-whisker plot and the box-and-whisker diagram. In descriptive statistics, a box plot or boxplot is a method for graphically demonstrating the locality, spread and skewness groups of numerical data through their quartiles. Box plot of data from the Michelson experiment Want to learn more about making data graphics? Become a member.Figure 1. That’s all there is to it, so the next time you’re thinking of making a bar graph or a histogram, think about using Tukey’s beloved box-and-whisker plot too. Basically, it gives you a good overview of the data’s distribution. For example, if there are more people who eat a lot of burgers than eat a few, the median is going to be higher or the top whisker could be longer than the bottom one. You can also see which way the data sways. The box-and-whisker of course shows you more than just four split groups. If more than one outlier ate the same number of hamburgers, dots are placed side by side. Dots represent those who ate a lot more than normal or a lot less than normal (outliers). Those in the top 25% of hamburger eating (713) are shown by the top “whisker” and dots. Take the top 50% of the group (1,426) who ate more hamburgers they are represented by everything above the median (the white line). We’ll sort those responses from least to greatest and then graph them with our box-and-whisker.
Let’s say we ask 2,852 people (and they miraculously all respond) how many hamburgers they’ve consumed in the past week. In any case, here’s how you read a box plot.
MINITAB BOXPLOT HOW TO
It could be that people don’t know about it or maybe are clueless on how to interpret it. The box plot, although very useful, seems to get lost in areas outside of Statistics, but I’m not sure why. Think of the type of data you might use a histogram with, and the box-and-whisker (or box plot, for short) could probably be useful. Tukey, used to show the distribution of a dataset (at a glance). The box-and-whisker plot is an exploratory graphic, created by John W.