Accuracy, precision, validity and reliability

In public health the terms accuracy, precision, validity and reliability mean the following:

Accuracy: The degree to which a measurement represents the true value of something. Simply put: How close a measurement is to the true value

Precision: The degree of resemblance among study results, were the study to be repeated under similar circumstances.                                                                          Simply put: How close the measurements are to each other

Lack of precision is referred to as ‘random error‘.

Validity:  The extent to which the study measures what it is intended to measure.       Simply put: Are the values describing what was supposed to be measured?

Internal validity: Are the results valid for the study subjects?

External validity (Generalizability): Are the results valid for the population from which the sample was drawn?

Lack of validity is referred to as ‘Bias‘ or ‘systematic error‘.

Reliability: A measure of how dependably an observation is exactly the same when repeated. It refers to the measuring procedure rather than to the attribute being measured. Simply put: Will one get the same values if the measurements are repeated? 

Note: Many authors use the terms in the following sense:

Accuracy (validity): Validity and accuracy are used synonymously

Precision (reliability): Precision and reliability are used synonymously






However, this article should help clarify the matter:

Useful Link:

Link to YouTube video explaining the concepts:


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