Discusses quartiles and medians, shows how to find them, and explains how they relate to box-and-whisker plots. Again, you can verify this number by using the QUARTILE.EXC function or looking at the box and whisker plot. Explains how to construct a simple box-and-whisker plot, and demonstrates the steps. This makes sense, the median is the average of the middle two numbers.Ħ. You can verify this number by using the QUARTILE.EXC function or looking at the box and whisker plot.ĥ. In this example, n = 8 (number of data points).Ĥ. This function interpolates between two values to calculate a quartile. For example, select the even number of data points below.Įxplanation: Excel uses the QUARTILE.EXC function to calculate the 1st quartile (Q 1), 2nd quartile (Q 2 or median) and 3rd quartile (Q 3). Most of the time, you can cannot easily determine the 1st quartile and 3rd quartile without performing calculations.ġ.
Box and whisker plots are great alternatives to bar graphs and histograms. You can easily see, for example, whether the numbers in the data set bunch more in the upper quartile by looking at the size of the upper box, as well as the size of the upper whisker. The left whisker represents the bottom 25 of the data, the left half of the box represents the second 25, the right. Note that the plot divides the data into 4 equal parts. As a result, the whiskers extend to the minimum value (2) and maximum value (34). Look at a box and whiskers plot to visualize the distribution of numbers in any data set. A box & whisker plot shows a 'box' with left edge at Q 1, right edge at Q 3, the 'middle' of the box at Q 2 (the median) and the maximum and minimum as 'whiskers'. the median is marked by a vertical line inside the box. In a box and whisker plot: the ends of the box are the upper and lower quartiles, so the box spans the interquartile range. As a result, the top whisker extends to the largest value (18) within this range.Įxplanation: all data points are between -17.5 and 34.5. A box and whisker plot (sometimes called a boxplot) is a graph that presents information from a five-number summary. Therefore, in this example, 35 is considered an outlier. A data point is considered an outlier if it exceeds a distance of 1.5 times the IQR below the 1st quartile (Q 1 - 1.5 * IQR = 2 - 1.5 * 13 = -17.5) or 1.5 times the IQR above the 3rd quartile (Q 3 + 1.5 * IQR = 15 + 1.5 * 13 = 34.5). In this example, IQR = Q 3 - Q 1 = 15 - 2 = 13. Q 3 = 15.Įxplanation: the interquartile range (IQR) is defined as the distance between the 1st quartile and the 3rd quartile. The 3rd quartile (Q 3) is the median of the second half.
The 1st quartile (Q 1) is the median of the first half. The median divides the data set into a bottom half. The x in the box represents the mean (also 8 in this example). Box Plot (also called as Box and Whiskers Plot) is a very popular and widely used plot for visualizing data in the field of Statistics and Data Analysis. On the Insert tab, in the Charts group, click the Statistic Chart symbol.Įxplanation: the middle line of the box represents the median or middle number (8).
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