Range and Spread
Grade 2What the range measures
Averages tell you the typical value of a data set. The range tells you how spread out the values are. A small range means the data clusters together; a large range means values vary a lot.
Range = highest value − lowest value
Worked example
EXAMPLE
Two students each sit five tests. Student A scores: 45, 48, 50, 52, 55. Student B scores: 20, 38, 50, 64, 78. Both have a mean of 50. Who is more consistent?
Student A range: 55 − 45 = 10.
Student B range: 78 − 20 = 58.
Both means are equal, but A has a much smaller range — A's scores are far more consistent. Student A is more consistent.
Comparing data sets
When you compare two data sets, talk about both a measure of average and a measure of spread. Just comparing means often misses the full picture — two data sets can have identical means but completely different ranges.
A typical exam comparison needs two sentences: one about average (who scored higher on average) and one about spread (who was more consistent or reliable).
Limitation of the range
The range depends entirely on the two extreme values. One unusually high or low result changes the range drastically, even if all the other values are tightly bunched together. That's why GCSE also uses the interquartile range — it ignores the extremes.
