Sometimes called a “box and whisker plot”, a box plot shows how the scale scores for a group of students are spread out across the range. The Year Group Report uses box plots to show how a group results compare with the achievement of a national reference sample for a particular year level.
The Box Plot
Median
This is the mid-point of the data and is shown by the line that divides the box into two parts. Half the scores are greater than or equal to this value and half are less.
Upper quartile
Seventy-five percent of the scores fall below this value, which is represented by the top of the box.
Lower quartile
Twenty-five percent of the scores fall below this value. This means 50 percent of the scores fall within the confines of the box between the upper and lower quartiles.
Upper and Lower Whiskers
The upper whisker shows the spread of the highest 25 percent of the scores and the lower whisker the spread of the lowest 25 percent of the scores.
The notch
The median for the school is not considered to be different from the reference group, if the notch around the reference group’s median overlaps with the line showing the school’s median.
Outlier
An outlier is a score that lies outside the extremes of the whiskers. It is considered an unusual score compared to the rest of the scores.
The box plots above show that students from NZCER School have achieved highly when compared with the national reference sample for Year 8. The lower quartile is higher than the national median.