Constructing a Box Plot with Data PointsĪ box plot provides a good summary of the data but it does not show individual data points. The median (Q2) is labelled with a line inside the box. The lower and upper quartiles are plotted at the positions of the start and end of the box. The maximum is the largest number in the list, which is 9.Ī box plot is constructed by labelling the minimum and maximum points at the whiskers of the plot. The minimum is the smallest number in the list, which is 1. This equals 6 and so, Q1 is found at the sixth number in the list. Q3 is found at position 3(n+1)/ 4, which for n=7 is position 3×(7+1)/ 4.This equals 4 and so, Q1 is found at the fourth number in the list. Q2 is found at position (n+1)/ 2, which for n=7 is position (7+1)/ 2.This equals 2 and so, Q1 is found at the second number in the list. Q1 is found at position (n+1)/ 4, which for n=7 is position (7+1)/ 4.There are 7 numbers in the list, so n = 7. Plot these quartiles along with the minimum and maximum points using lines and connect them to make a box.įor example, construct a box plot from the data in the list 1, 3, 5, 6, 6, 7, 9. These quartiles are found at the (n+1)/ 4, (n+1)/ 2 and 3(n+1)/ 4 positions, where n is the number of data points in an ordered list. To construct a box plot from a list of data, first calculate the first, second and third quartiles.
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How to Construct a Box Plot from a List of Data These whiskers are connected to the box portion of the box plot. The position of the minimum and maximum are shown with lines, called whiskers. Draw lines to indicate the position of the maximum and minimum and connect these lines to the box We draw lines in line with the values at Q1 and Q3. Draw lines to indicate the position of the lower and upper quartiles Draw lines to indicate the position of the minimum and maximum and connect these lines to the box.įor example, construct a box plot for the following data:.Draw a line inside the box to indicate the position of the median.Draw lines to indicate the position of the lower and upper quartiles.How to Construct a Box Plot To construct a box plot: The larger the interquartile range, the more spread the middle 50% of data is. The larger the range, the more spread the whole data is. Both the range and interquartile range are used to describe the spread of data. The spread of data refers to how spread out the numbers in the data are. The larger the interquartile range, the more spread the middle 50% of the data is. The larger the range, the more spread the data is. The larger median, the larger the average. The median is found at the position of the line inside the box. The lower and upper quartiles are located at the upper and lower edges of the box portion of the plot. The minimum and maximum are located at the ‘whiskers’ of the plot. Read the median which is in line with the line inside the box.Ī box plot is also known as a box and whisker plot.Read the upper quartile which is in line with the end of the box.Read the lower quartile which is in line with the start of the box.Read the maximum value in line with the last line.Read the minimum value in line with the first line.How to Read a Box Plot To read a box plot: Side-by-side box plots allow for two or more data sets to be compared in a graphical form. From this, the spread and skew of the data can also be seen. The distribution of data is shown through the positions of the median and the quartiles. In statistics, a box plot is used to provide a visual summary of data. Box plots are a useful way to compare two or more sets of data visually. From this, the range, interquartile range and skewness of the data can be observed. A box plot indicates the position of the minimum, maximum and median values along with the position of the lower and upper quartiles. A box plot is a diagram used to display the distribution of data.
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