Precision and Accuracy: Key Terms

The central value for a set of measurements is usually the same as the individual results.

The mean and the median are both used as measures of central value.

The median is the average value of all the results in a set.

When there is an odd number of results, the median is the middle result when data are arranged in order.

Replicates in a sample are not important for determining the reliability of results.

The mean is calculated by summing up all replicate measurements and multiplying them by the number of measurements.

Precision measures the closeness of results obtained in different ways.

Accuracy indicates the agreement between a measurement result and the true value.

Random error causes data to be scattered symmetrically around the mean value.

Systematic errors may be either random or indeterminate.

Personal errors in measurements require personal judgments.

Constant errors become less serious as the size of the quantity measured decreases.

Proportional errors are caused by the presence of interfering contaminants in the sample.

The effect of solubility losses is an example of proportional errors.

Accuracy is expressed in terms of absolute error only.

Systematic method errors are introduced by instrumental errors.