7.5 Precision

Precision is the closeness of agreement between indications or measured quantity values obtained by replicate measurements on the same or similar objects under specified condition. In EDXRF, the precision of a measurement with a result of N counts is influenced by the statistics nature of counting process . Therefore, precision in the determination of the element weight fraction w_i is directly proportional to the square root of the measurement time t_meas and to the instrumental sensitivity S_i . It is also evident that the relative precision improves with the increase in elemental weight fraction w_i.

The overall precision can also include the contribution of other experimental factors (differences in sample positioning, stability of excitation flux intensity, among others) and must be assessed as the standard deviation σ(N) of k replicate measurements N_i rather than relying only on that arising from the counting statistics itself.