What is precision?

Let’s go back to our classroom example. To compare average test scores between students with work experience and those without, we calculated the average difference between those scores. That calculation gave us the number 0.  

Precision reflects how well your calculated average difference – that 0 from our example – reflects the “true” average difference.

In other words, does our estimated number really reflect the true average difference between the math scores of older and younger students? Or, are these classroom scores somehow different from other classrooms?

To calculate precision, you take into account two factors –

1. The difference between each individual test score and the average test score

2. The number of scores that are being averaged

To try to understand these two components, let’s look at another math score question.