Anomalous Readings (Edexcel International A Level (IAL) Physics): Revision Note

Anomalous Readings

• 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 much larger difference from the mean than the rest of the results — there is no fixed percentage test

  • A value is anomalous only when the gap between it and the other readings is much larger than the spread of those readings among themselves

  • If that spread can be explained by how the measurement was taken, e.g. hand-timed values that differ by less than a typical reaction time of about 0.2 s, there is no anomaly, and every value goes into the mean

• The results or ‘data’ collected from an experiment can be made more precise 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:

  • Exclude this value when calculating the mean

  • Repeat this measurement

• Note: In the exam, only leave a value out of the mean when it is clearly anomalous — otherwise you should use all the tabulated readings