Lesson - Quartiles
Learning Intention: define quartiles and demonstrate use of quartile ranges for analysing data.
Diagnostic:
Explanation:
Quartiles are the values that divide an ordered data set into four (approximately) equal parts.
There are three quartiles:
The lower quartile (Q1) divides off (approximately) the lower 25% of data values.
The second quartile (Q2) is the median.
The upper quartile, (Q3) divides off (approximately) the upper 25% of data values.
Inter-Quartile range
When there are outliers in the data, it is more appropriate to calculate the interquartile range.
The interquartile range is the range of the middle half of the data.
interquartile range = upper quartile – lower quartile
E.g. 7 - 4 = 3
We can show the quartiles and inter quartile range on a box and whisker plot:
Example:
Tasks:
1) Using an analysis you have completed previously, calculate the upper and lower quartiles and draw a box and whisker plot over the top of your box plot.
Diagnostic answers: