William Horwitz (1918 – September 27, 2006, in Olney, Maryland) was an analytical chemist who is notable for formulating a description of the relationship between the variability of chemical measurements and the concentration of the analyte. This relationship, called the Horwitz curve applies only to the between-laboratory variability of measurements.
w = weight percent of analyte in sample [%-w/w]
C = mass fraction of analyte in sample [dimensionless] = w / 100%-w/w
predicted RSD (relative standard deviation) = 2^(1-0.5*log(C))%