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Statistics 101

Introduction
Quartiles
4. Quartiles – computing methods
Percentiles
Quantiles
Standard Deviation and Variance

Instruction

Unfortunately, there is no strict rule for computing quartiles. Different methods give different results. One of the most commonly used methods is the following:

Explanation Graph


Let's calculate the quartiles for the following set:

1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13

We already know how to calculate the median (the middle quartile); it's 7. Below this point, we have half the data \{1, 2, 3, 4, 5, 6\}. The median of this subset (and therefore the lower quartile of the entire set) is 3.5. The median of the upper subset (and thus the upper quartile of the original set) is 10.5.