Precision, Accuracy, Reliability, and Validity

Match the following

• Accuracy

• How close repeated measurements are to each other (consistency of values).

• Validity

• How close a measurement is to the true value.

• Confidence

• Whether results are repeatable across different trials and experiments.

• Precision

• How sure we are that results show a real trend and are not due to chance.

• Reliability

• Whether the experiment is a fair test—only the independent variable affects the results.

Match the following

• Reliability

• A thermometer reads 100.0°C for boiling water, which is correct.

• Accuracy

• A student measures boiling water three times and gets 99.8°C, 99.9°C, and 99.8°C.

• Validity

• Dropping a ball multiple times on different days from the same height gives similar results each time.

• Precision

• Testing how fertiliser affects plants, but some plants get more sunlight than others.

An error that shifts all measurements in the same direction (higher or lower than the true value). - ​ ​ (a)  

An error that varies unpredictably from measurement to measurement. - ​ (b)  

It affects accuracy. - ​ (c)  

It affects precision. - ​ (d)  

• Systematic Error
• Random Error

A student wants to determine how fertiliser affects plant growth. They apply fertiliser to one plant and measure its height after two weeks using a ruler.

The ruler is properly calibrated, and measurements are taken always in the same way.

Which of the following are true about this experiment? (Select all that apply)

• The experiment lacks reliability because it was only done on one plant.

• The experiment lacks validity because other factors (e.g., sunlight, water) may also affect growth.

• The results are precise because the student only measured one plant.

• The experiment is accurate because it correctly measures plant height.

A student is testing how acidic a river is. They collect one water sample and use a pH meter to measure the pH three times, carefully recording the readings.

The pH meter is properly calibrated.

Which of the following are true? (Select all that apply)

Consider the scientific definitions of precision and reliability, not the IGCSE ones.

• The results improve precision by reducing the effect of random errors.

• The results do not test reliability because they only measure the same sample.

• The results are accurate because the pH meter is properly calibrated.

• Technical replicates can replace the need for true replicates.

A student wants to investigate whether stretching before exercise affects how far someone can jump.

They ask one person to jump six times:

• - Three without stretching

• - Three after stretching

• They then calculate the average jump distance for each condition.

Which of the following statements are true? (Select all that apply)

Consider the scientific definitions of precision and reliability, not the IGCSE ones.

• These are technical replicates, which improve precision but do not confirm reliability.

• To confirm reliability, the student should repeat the experiment with multiple people (true replicates).

• Taking multiple measurements from the same person is enough to prove the experiment is reliable.

• If different people show similar trends (longer jumps after stretching), this increases the accuracy of the results.

A student investigates how far a person can jump.

They ask one person to jump five times, carefully measuring the distance each time.

The results are very similar across all five trials.

Based on this information, determine the following:

Precision:​ (a)  

Accuracy: ​ (b)  

Reliability (in science): ​ (c)  

Reliability (in IGCSE): ​ ​ (d)  

• High
• Unknown
• No effect

Answer explanation

Why?

• Precision is high because the results are very similar across repeated trials.

• Accuracy is unknown because we don’t know if the measuring tool is correct or if systematic errors exist (e.g., miscalibrated tape measure).

• Reliability is low because the experiment was only done with one person, meaning we cannot confirm the results apply to everyone.

A student investigates how far a person can jump.

They ask one person to jump five times, carefully measuring the distance each time.

This time, they use a more precise ruler to measure the jump distance, ensuring finer increments in measurement.

Based on this information, determine the following:

Precision:​ (a)  

Accuracy:​ ​ (b)  

Reliability (in science):​ (c)  

Reliability (in IGCSE):​ ​ (d)  

• No effect
• Improves
• Unknown

Answer explanation

Why?

• Precision improves because a more precise ruler reduces small measurement errors (more decimal places).

• Accuracy is unknown because we don’t know if the ruler is correctly calibrated (a systematic error could still exist).

• Reliability is not affected because using a more precise ruler does not test whether the results are repeatable in different trials or for different people.

A student investigates how far a person can jump.

Instead of testing just one person, they measure the jump distance of 10 different people and observe a consistent trend—for example, taller individuals tend to jump farther.

Based on this information, determine the effect on:

Precision:​ (a)  

Accuracy:​ ​ (b)  

Reliability (in science):​ (c)  

Reliability (in IGCSE):​ ​ (d)  

• No effect
• Improves
• Unknown

Answer explanation

Why?

• Precision does not improve because using more participants does not reduce variability in individual measurements—precision relates to how consistent measurements are within a single person’s trials, not across different people.

• Accuracy remains unknown because we don’t know if the measuring tool is correctly calibrated or if systematic errors exist (e.g., incorrect tape placement).

• Reliability improves because testing multiple participants (true replicates) ensures that results apply to a wider population and are not just a coincidence.

A student investigates how far people can jump.

This time, they measure the jump distances of 10 different people and calculate the average jump distance.

Assuming there are no systematic errors, how does taking the average affect the results?

• It decreases accuracy because the measurements are different.

• It has no effect on accuracy because the same measuring tool is used.

• It improves reliability by reducing the impact of random errors in individual measurements.

• It improves precision but not accuracy

Answer explanation

✅ Averaging primarily improves reliability because it makes results more consistent and reproducible.
✅ It may improve accuracy, but only if errors are mostly random and not systematic.