Horwitz equation

The Horwitz equation was developed based on a large number of collaborative studies (interlaboratory trials). It was discovered that there was an empirical relationship between the concentration of an analyte and the precision obtained by experienced analysts: at low concentrations the precision decreases. This equation gives only an impression of what average precision you can reasonably expect at a certain concentration level. It does not tell you what the precision exactly has to be, because that may vary depending on the compound and method.

Remember that a high coefficient of variation (CV) means a low precision.