Explaining the difference between accurate and reliable True value Imagine we carried out an experiment . The Bulls Eye represents the true value if there were no errors in your experiment.

Meaning of accurate and reliable 1 Imagine then – if the first person did this experiment 4 times and got the following results. The results of this experiment are very close together. The results are reliable but they are NOT ACCURATE because they are far away from the true value.

Meaning of accurate and reliable 2 Imagine then – if the second person did this experiment 4 times and got the following results. Now our results are close to the true value but also very close together around the true value. We say it is both RELIABLE and ACCURATE.

Meaning of accurate and reliable 3 Imagine then – if the third person did this experiment 4 times and got the following results. Now our results are all over the place and not close to the true value. The results are NOT RELIABLE nor are they ACCURATE.

Meaning of ANOMALOUS result Imagine now the first person then did the same experiment for the 5TH time and got the following result. 5th reading – this is an ANOMALOUS result. It doesn’t seem to follow the pattern . We would normally REPEAT this particular result or ignore it when we do an average. First 4 readings

Example of reliable data Imagine the teacher has carried out the experiment first and used a light gate! The teacher’s value was 3.25s. Student 1 result: Height parachute dropped from (m) Time taken to drop height 1st reading (seconds) repeat 1 repeat 2 Repeat 3 1.0 3.5 3.3 3.1 the data are reliable because they are very close together. It is also accurate because it is close to the answer that is expected. Close together

Example 2 Anomalous result The teachers value was 3.25 seconds. Student 2 result: Height parachute dropped from (m) Time taken to drop height 1st reading (seconds) repeat 1 repeat 2 Repeat 3 1.0 3.5 3.4 3.3 8.2 Far away from the others This set of data is still reliable - we can be pretty sure that the answer that we are looking for lies near 3.x but there is an anomalous result which will skew the average towards a higher value than it really is in this case. Average will be higher than it actually is

Example 2 Anomalous result To correct this mistake we can either repeat the last mistake or ignore it when we work out an average. Height parachute dropped from (m) Time taken to drop height 1st reading (seconds) repeat 1 repeat 2 Repeat 3 1.0 3.5 3.4 3.3 Result ignored By removing the anomalous – the average value will move closer to the true value i.e. it will become more accurate Average will be more accurate when anomalous is removed

Meaning of accurate and reliable 3 Student 3 result: Height parachute dropped from (m) Time taken to drop height 1st reading (seconds) repeat 1 repeat 2 Repeat 3 1.0 1.5 6.4 5.3 2.2 The teachers value was 3.25s. Results are all over the place The results are NOT RELIABLE nor are they ACCURATE.