Recognising random error
Random error appears when repeated readings vary unpredictably. Changes that cannot be fully controlled, such as variations in experimental conditions, can produce this scatter.
Random error mainly affects precision. Greater random variation gives a wider spread of readings around their mean value.
Repeated readings reveal random variation because individual measurements fluctuate rather than all giving the same value.
Reducing its effect
- Take several repeat readings and calculate a mean.
- Use the repeated values to identify any anomalous result.
- Where appropriate, use a data logger or camera to reduce variation associated with judging a reading manually.
- Choose apparatus that can resolve the size of change being measured; for very small lengths, a micrometer is preferable to a millimetre ruler.
Exam Tip: When asked how to reduce random error, state that the measurement should be repeated several times and a mean calculated.