Accuracy, precision and error

Four words that are not synonyms, and questions test whether you know the difference.

What it is

Accurate means close to the true value. Precise means repeat readings are close to each other. Repeatable means the same person gets the same results; reproducible means someone else does. Resolution is the smallest change an instrument can show.

Where it applies

All three sciences, in every practical question.

How it works

Results can be precise and wrong — a mis-zeroed balance gives tightly clustered readings that are all 2g out. That is a systematic error, and repeating does not fix it.

Random error scatters readings either side of the true value and IS reduced by repeating and taking a mean.

An anomalous result is one that does not fit the pattern; it should be identified and excluded from the mean, not quietly deleted.

How to use it in your work

Use the right word. Saying "more accurate" when you mean "more precise" loses the mark.

When asked how to improve a method, distinguish which kind of error you are addressing.

Anomalies: say you would repeat that reading, and exclude it from the mean — and say both.

Where to get help

Your teacher, your board's specification for the depth required at your tier, and Bitesize for the diagrams. The subject song runs the topics in order.