Definition of Variation, observer

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Variation, observer: Failure by the observer to measure accurately, resulting in error.

Observer variation may be due to the observer's missing a measurement, making an incorrect measurement, or misinterpreting data.

Inter-observer variation is the amount of variation between the results obtained by two or more observers examining the same material. Intra-observer variation is the amount of variation one observer experiences when observing the same material more than once.