Monday, June 12, 2017

How to make a Box Plot

Box Plots 

One of the things I struggle most with in math is box plots. They always confuse me because the middle of the data is almost never in the middle of the graph.

What is a Box Plot?

The first thing you need to know, is what a box plot is. A box plot is a graph that shows data based on the five number summary (minimum, first quartile, median, third quartile, maximum). These words are sometimes confusing, so here are their definitions.

Minimum - The smallest number in a set of data

First Quartile - The middle value of the first half of the data

Median - The middle number of the entire set of data

Third Quartile - The middle value of the second half of the data

Maximum - The greatest number in a set of data

Finding the 5 Number Summary

Now that we know what a box plot is, lets start making one. The data we have to use is:

1, 1, 1, 2, 4, 6, 7, 9, 11, 12, 13, 15, 17, 17, 19

The first thing we need to do is find the median. We do this by counting down from the sides. The median in this set of data is 9. The next thing we need to do is find minimum and maximum. We can do this by finding the largest number and smallest number in the data. The minimum in the data is 1, the maximum is 19.   Next is the first and third quartile. The first quartile is 2, the third is 15. Now we put these values on a number line.

             I       I                                                   I                                            I                             I
Image result for 1 number line to 20
The next step is to connect all the values with a line. Finally, create a box that starts at the first quartile, and ends at the third quartile.