Processing data starts with checking it. Look along each row of repeats for anomalous values that are far from the others. Exclude them, giving a reason, before calculating the mean. The mean is the best estimate of the true value.
The range of the repeats indicates the spread. Half the range is often used as a simple estimate of uncertainty: a mean of 24 s with a range of 4 s can be written 24 ± 2 s. Results with smaller uncertainty are more precise. Recording to a consistent number of decimal places shows the resolution of the instrument.
Worked example
Repeats: 41, 43, 55, 42 s. Find the mean without the anomaly.
- 55 s is far from the others: it is anomalous.
- Mean = (41 + 43 + 42) ÷ 3 = 126 ÷ 3.
Answer:Mean = 42 s.
Key words
- anomaly
- a result that does not fit the pattern
- uncertainty
- the likely spread around a value
- precise
- repeats close together
- resolution
- the smallest change an instrument can show
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