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The coefficient of variation as a measure of spectrophotometric repeatability
Author(s) -
Centore Paul
Publication year - 2016
Publication title -
color research and application
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.393
H-Index - 62
eISSN - 1520-6378
pISSN - 0361-2317
DOI - 10.1002/col.22002
Subject(s) - repeatability , standard deviation , measure (data warehouse) , coefficient of variation , sample (material) , multiple criteria decision analysis , sample mean and sample covariance , wavelength , statistics , mathematics , standard error , optics , chromatography , computer science , chemistry , data mining , physics , operations research , estimator
The mean color difference from the mean (MCDM) is a standard measure of spectrophotometric repeatability. This article proposes a supplementary measure: the coefficient of variation (CoV), which is the ratio of the standard deviation of the measured reflectances to their mean. The CoV is calculated from the same repeated sample measurements as the MCDM. Unlike the MCDM, the CoV depends only on physical quantities, and not on perceptual quantities; furthermore, a CoV is defined for each wavelength. This article analyzes data from six different spectrophotometer–sample combinations. An important empirical result is that the CoV is nearly constant across wavelengths, except when the reflectance at a particular wavelength is less than about 5%, in which case, measurement variability is markedly greater. Because the MCDM tends to lose this fact through averaging, the CoV is recommended as an adjunct to the MCDM for spectrophotometer analysis and development. The CoV analysis also provides evidence that samples’ surface geometry is a major factor in measurement variability. © 2015 Wiley Periodicals, Inc. Col Res Appl, 41, 571–579, 2016