- Experimental errors (also known as operator errors or ‘one off’ errors) will affect the results of an experiment and can produce anomalies
- These anomalies should be identified during the evaluation of results and before drawing conclusions
- Anomalies can be identified by looking for results or data points on a graph that do not fit with the trend or with other repeat readings carried out during the experiment
- These anomalous results will show a larger difference from the mean than the rest of the results (a result is often taken to be anomalous if it differs from the mean result by more than 10%)
- The results or ‘data’ collected from an experiment can be made more reliable if the experiment is repeated several times and anomalies are removed
- This, in turn, allows more valid conclusions to be drawn
- Anomalous results are always inconsistent with other readings e.g., a point that is not on the line of best fit of a graph
Identifying an anomalous result from a graph
- If an anomaly occurs in the experiment:
- Ignore this value when calculating the mean
- Repeat this measurement
A student achieves a set of repeat readings for the current through a bulb.
|2.5 mA||2.8 mA||6.1 mA||2.0 mA||2.3 mA|
Calculate the mean current through the bulb.
1. Identify the anomalous result
- The only result that doesn't fit with the rest of the data is 6.1 mA
- This can be ignored when calculating the mean
2. Calculate the mean current
Mean current = = 2.4 mA
When calculating the mean of some repeat readings for data given in your practical paper, always ignore any anomalous readings that are inconsistent when calculating the mean.