Quartile and Box Plot

Box Plots/Box and Whiskers

It is another way to represent data.  We have already used Dot Plots and Histograms to represent data.  Box Plots are an easy way to show if a number is above the middle of data or below the middle of data.

5 Number Summary

We use the 5 number Summary (5 special data number) to create and help interpret data from a box plot.  The 5 number summary includes:  Minimum, Maximum, (Q1) Quartile 1 or Lower Quartile, (Q2) Median, and (Q3) Quartile or Upper Quartile.

Parts of a Box Plot

• Min – Minimum: Smallest number of the Data Set

• Max – Maximum:  Largest number in the data set

Parts of a Box Plot

• Q1 – Lower Quartile:  The median of the lower half of the data

• Q2 – Median:   Middle number of the set of data

• Q3 – Upper Quartile:  The median of the upper half of the data

• Interquartile Range (IQR): Q3 – Q1

Quartiles

• Quartiles divide the data set into four equal parts.

• 25% each

Median

• Divides the data set into two halves

• 50% of the data numbers are below this number

• 50% of the data numbers are above this number

Constructing Box Plots

Before determining your quartiles, mean, and median, make sure to order all values in the data set from the least to greatest. If you don't. the data will be skewed and