Accuracy
A measurement result is considered accurate if it is judged to be close to the true value.
Calibration
Marking a scale on a measuring instrument. This involves establishing the relationship between indications of a measuring instrument and standard or reference quantity values, which must be applied. For example, placing a thermometer in melting ice to see whether it reads zero, in order to check if it has been calibrated correctly.
Data information
either qualitative or quantitative, that has been collected.
Error
See also uncertainty.
Measurement error
The difference between a measured value and the true value.
Anomalies
These are values in a set of results which are judged not to be part of the variation caused by random uncertainty.
Random error
These cause readings to be spread about the true value, due to results varying in an unpredictable way from one measurement to the next. Random errors are present when any measurement is made, and cannot be corrected. The effect of random errors can be reduced by making more measurements and calculating a new mean.
Systematic error
These cause readings to differ from the true value by a consistent amount each time a measurement is made. Sources of systematic error can include the environment, methods of observation or instruments used. Systematic errors cannot be dealt with by simple repeats. If a systematic error is suspected, the data collection should be repeated using a different technique or a different set of equipment, and the results compared.
Zero error
Any indication that a measuring system gives a false reading when the true value of a measured quantity is zero, eg the needle on an ammeter failing to return to zero when no current flows. A zero error may result in a systematic uncertainty.
Data
Data which has been shown to be valid.
Fair test
A fair test is one in which only the independent variable has been allowed to affect the dependent variable.
Hypothesis
A proposal intended to explain certain facts or observations.
Interval
The quantity between readings, eg a set of 11 readings equally spaced over a distance of 1 metre would give an interval of 10 centimetres.
Precision
Precise measurements are ones in which there is very little spread about the
Accuracy
A measurement result is considered accurate if it is judged to be close to the true value.
Uncertainty
Uncertainty The interval within which the true value can be expected to lie, with a given level of confidence or probability, eg ‘the temperature is 20 °C ± 2 °C, at a level of confidence of 95%’.
Resolution
This is the smallest change in the quantity being measured (input) of a measuring instrument that gives a perceptible change in the reading.
Repeatable
A measurement is repeatable if the original experimenter repeats the investigation using same method and equipment and obtains the same results. Previously known as reliable.
Reproducible
A measurement is reproducible if the investigation is repeated by another person, or by using different equipment or techniques, and the same results are obtained. Previously known as reliable.
Validity
Suitability of the investigative procedure to answer the question being asked. For example, an investigation to find out if the rate of a chemical reaction depended upon the concentration of one of the reactants would not be a valid procedure if the temperature of the reactants was not controlled.
Precision
Precise measurements are ones in which there is very little spread about the mean value. Precision depends only on the extent of random errors – it gives no indication of how close results are to the true value.
Random error
an error in measurement caused by factors which vary from one measurement to another.
Systematic error
an error having a non-zero mean, so that its effect is not reduced when observations are averaged.
Anomaly
something that deviates from what is standard, normal, or expected.
