Confusing accuracy and precision

Why it matters

Posted by hossg on December 07, 2023 · 2 mins read

Too many people confuse precision and accuracy, for a variety of reasons, and often with significant consequences.

Of course sometimes people simply don’t know the difference in terminology, so let’s clear that up straight away.

Accuracy in a prediction, measurement or description, is the extent to which your description does indeed correspond to reality: whether it is or is not a correct description.

Precision on the other hand is the degree to which your description is consistent and repeatable, and it can act as a measure of the confidence you can have in your description.

A common analogy is that of a target board. Accuracy is akin to how close on average your arrows land to the bullseye, regardless of how close they are to each other. Precision is like shooting several arrows and having them all land close to each other, even if they are not near the bullseye.

The real issue though is not one of vocabulary, but one of behaviour. There’s often a significant cost to improve precision, whether in terms of time and effort, or in terms of distracting attention from getting an accurate answer! It is certainly worth thinking about whether improved precision actually helps you make the decisions you are considering. If not, don’t bother chasing useless further precision!

Of course, more precision can help give you confidence in the accuracy, but if the greater precision or more confidence won’t make a meaningful difference to your decision-making, then why bother?

Some people use this as a means of not making an uncomfortable decision, or as a way of avoiding being seen to take a position.

When presented with data, a business case, or an explanation, they ask for more detail or precision. They deflect the cost of chasing greater precision onto others, and remain safe from their discomfort. It is easy to ask for more; it’s far harder to accept the precision you are presented with and make decisions or take positions nonetheless.

Making decisions with less-than-perfect information is hard; it involves judgement and risk, and it truly requires understanding the difference between precision and accuracy. And so it turns out that words do matter, but to know which word to use, you have to understand the concepts behind them.