Chemical measurements

Accuracy

Is a measure of the closeness of agreement between an individual test result and the true value.

Precision

Is the closeness of agreement between independent measurements obtained under the same conditions.

Random error

Is a chance difference between the observed value and the true value of something.

Mainly affect precision

Systematic error

Is consistent or proportional difference between the observed and true values of something

Mainly affect accuracy

Ways of reducing random errors

• Take repeat measurements

• Calculate mean

• Control variables

Repeatability

Is the precision obtained when measurement results are produced over a short timescale by one person (or the same group) using the same equipment in the same place

Reproducibility

Is the precision obtained when measurement results are produced over a wider timescale by people using equivalent equipment in different (but equivalent) places.

Resolution

Is the smallest change in the quantity being measured that can be detected by an instrument.

Uncertainty

is an estimate attached to a measurement which characterises the range of values within which the true value is asserted to lie.

Percentage uncertainty