Practicals – reliability, accuracy, validity and errors

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ACCURACY (exactness)

Most measurements contain some uncertainty. Accuracy refers to the exactness of a measurement.
We can measure a small distance with a metre rule or with much greater accuracy using a micrometer.

RELIABILITY (dependability)

Reliability refers to the consistency with which we can confirm a result. Consistency is usually achieved by repetition.

VALIDITY (fairness)

A procedure is valid if it tests what it is supposed to be testing. A procedure is invalid if the method of the experiment is incorrect or partially incorrect.
In a valid experiment all variables are kept constant apart from those being investigated, all systematic errors have been eliminated and random errors have been reduced by taking multiple measurements.
In determining validity, students should consider the degree to which evidence supports the assertion or claim being evaluated. This may be done by making comparisons or conducting further experiments.

first-hand information and data

secondary information and data

Accuracy Instruments should be precise and calibrated. Sources should be reputable?
Reliability All tests should be repeated a significant number of times. Information obtained should be consistent with information from other reputable sources.
Validity Experiments should test the hypothesis that is proposed.The experimental method must be correct?All variables should be identified and controlled. Information should be gathered in an unbiased and professional manner.Findings must relate to the hypothesis or problem.


The two different types of error that can occur in a measurement are:

1. Systematic error – this occurs to the same extent in each measurement. EG when the needle of a voltmeter is not correctly adjusted to zero when no voltage is present.

2. Random/Human error – this occurs in any measurement as a result of the variations in measurement technique. Eg parallax error, limit of reading.