What are accuracy and precision?

It is important that the results from scientific experiments are both accurate and precise.

This means that the data collection needs to be accurate and precise as well.

This way, we can be more confident that our results are correct.

When results aren't accurate or precise they are called inaccurate or imprecise.

• Accurate measurements are those which are closest to what they should be.

• Precise measurements are those which have been repeated and are similar.

• Inaccurate or imprecise measurements are those that are neither accurate nor precise.

• Scientists at The Lawrence Berkeley National Laboratory in California are able to use an electron microscope which can observe objects using a resolution of just one ten-millionth of a millimetre. That’s narrower than a single hydrogen atom.

• Spacecraft have to be accurate and precise over very long distances. NASA's New Horizons probe journeyed successfully from Earth to Pluto via Jupiter, a journey of over 5.3 billion kilometres.

• Scientists in America have built an atomic clock which is so precise. it loses just one second every 300 billion years!

• Although magnetic compasses are usually accurate and always point north, the Earth's actual north magnetic pole is constantly moving over time due to changes in the Earth's outer core.

Accurate measurements are those which are close to what they should be. We know that the temperature of water's boiling point is 100°C. An accuratethermometer will give us this value.

Taking repeat readings or measurements when needed will increase the accuracy and reliability to help you to spot any anomalies.

Think of accuracy like an archery game, with a bow and arrow. If you aim for the centre of the target and hit it, that's accurate.

If you keep hitting the same spot every time but that spot is far from the centre of the target, you are precise, but not accurate!

An example of accuracy

Imagine you're measuring the length of a table using a ruler.

If the actual length of the table is 1.5 metres (m) and your measurement is 1.5m, you are accurate.

However if you measure it as 1m then that would not be accurate.

Science experiments are often repeated several times.

Precisemeasurements are those that have been repeated and are similar.

If you timed yourself swimming a length in a pool several times and you recorded similar results, they would be precise.

An example of precision

If you measure the length of a table three times and record1.49 metres (m) each time, then you are precise because your measurements are very close to each other.

However, if the true length of the table is 1.5m, then your measurements aren'taccurate.

Accuracy – Measurements that are close to what they should be.

Anomalies – Something that is not expected or different from previous results.

Data collection – The process of collecting and evaluating data.

Experiments – Scientific procedures that produce results.

Inaccurate – Lacking accuracy or precision.

Imprecise – Lacking precision or accuracy

Measurements – Scientific procedures that produce results.

Precise – Measurements that have been repeated and are similar.

Reliability – Whether something can be trusted or not.

Thermometer – A piece of scientific equipment that measures temperature.

Ask a responsible adult to help you with this activity.

You will need a large piece of paper and some small balls.

1. Draw a giant target onto the large paper.
2. Throw the balls at the paper and try to make different patterns.
3. Explain why each one is accurate or not, and why it is precise or not.

What other scientific investigations could you complete using the same equipment?