Using numbers and handling data
Using numbers and handling data

Start this free course now. Just create an account and sign in. Enrol and complete the course for a free statement of participation or digital badge if available.

Free course

Using numbers and handling data

2 Accuracy, precision and common errors

2.1 Differences between accuracy and precision

Accuracy is a measure of how close a result is to the true value. Precision is a measure of how repeatable the result is. For instance, a group of three friends tried the shooting gallery at a fair and their targets are shown in Figure 6. The first person was an expert marksman, but they were using a rifle with sights that had not been set properly. Although they aimed the sights at the bull's-eye they consistently hit the target off to the left side instead. They were not accurate, but they were precise. The second person was also an expert marksman, but noticed the incorrectly set sights and compensated by aiming to the right of the bull's-eye. Consequently, all their shots hit the centre of the target - they were both accurate and precise and their results were good. The third person was hopeless with the rifle and their shots landed all over the target - they were neither accurate nor precise.

Figure 6
Figure 6 Target practice analogy, demonstrating the difference between accuracy and precision. Low accuracy but high precision = systematic error. High accuracy and high precision = good results. Low accuracy and low precision = bad results

From the example given you can see how it is possible to be very precise, but not at all accurate. This is called a systematic error (sometimes also called bias) and can normally be corrected.


Take your learning further

Making the decision to study can be a big step, which is why you'll want a trusted University. The Open University has 50 years’ experience delivering flexible learning and 170,000 students are studying with us right now. Take a look at all Open University courses.

If you are new to University-level study, we offer two introductory routes to our qualifications. You could either choose to start with an Access module, or a module which allows you to count your previous learning towards an Open University qualification. Read our guide on Where to take your learning next for more information.

Not ready for formal University study? Then browse over 1000 free courses on OpenLearn and sign up to our newsletter to hear about new free courses as they are released.

Every year, thousands of students decide to study with The Open University. With over 120 qualifications, we’ve got the right course for you.

Request an Open University prospectus371