Repeat Readings
- Experiments commonly require repeat readings
- This improves the accuracy of a measurement, that is dependent on the quality of the measuring instruments used to determine it, as well as the skill of the scientists involved
- Repeat readings also means the data is considered reliable
- The spread of the readings should be as small as possible to be precise
- This ensures the measurements are not just by luck or random
- Repeat readings also allows you to identify any anomalous results
- This is a result that doesn't fit in with the pattern of readings
- It is appropriate to have repeat readings where possible in an experiment, and to leave sufficient space in data tables to accommodate these
- The average value of that variable should always be found from the repeat readings to use in further calculations
A table of results with space for repeat readings
- It may not be best to repeat readings every time for all experiments
- This should be decided on how easy it is to take the readings in the first place
- For example, electrical components heat up from current after a while which could affect the results
- Therefore, for each reading the components should be disconnected from the power supply to cool down
- When they are reconnected again, the whole experiment needs to be repeated to get the repeat reading. This could take too long, especially for a wide range for the independent variable
- There could also be difficulty getting repeat readings for a time dependent variable
- This is because time will pass between the readings
- For example, if you want to measure a dependent variable at certain time of day (e.g., between 6am-7am), the whole experiment will have to be repeated the following day, and the next and so on, which may not be in the scope of the time allowed for the experiment
Worked example
A student is asked to determine the power of another student who runs up some stairs.
Comment on whether repeat readings are appropriate in this case.
- The student may become tired so their speed could change as they lose energy
- The experiment will have to be repeated after rest, after their heart rate gets back to a regular level
- The height of the stairs should be measured before each reading to check whether it stays the same
- There could be difficulty of starting and stopping the stopwatch to measure the time because of reaction time
Examiner Tip
When asked to discuss repeat readings, think about how easy it would be to take those repeat readings (commonly between 3-5 times). If it is just connecting up a circuit, or letting a pendulum oscillate, this could be quite simple. If there are possible changes that could happen to the apparatus or environment of the experiment between taking these repeat readings, then taking repeats straight away would not make it a fair test, therefore it could be best not to do so.
Remember that you will always need to take a wide range of readings (between 5-10) and experiments will have to be completed in a certain amount of time. If each reading takes 1 minute, and you are taking 10 readings, if these are all repeated 3 times this could make the experiment 30 minutes long, compared to 10 minutes!
