Abstract
A breakthrough in scientific understanding about
multivariate calibration & measurement has recently
created the method of science-based calibration ("SBC").
Multivariate measurements are not fundamentally different
from the univariate case; rather, the two cases
correspond one-to-one in every aspect. The significant
advantages provided by SBC to the calibration of process
analyzers will be shortly reviewed. Following this, the
focus will be on the conclusions that can be drawn when
applying the scientific understanding generated by SBC to
the existing methods of calibration. The results are
concerning. A fair estimate is that several ten per cent
of PLS and PCR calibrations are not purely measuring what
people think they are measuring. (A peer-reviewed
publication about these findings is in preparation.)
The correct mathematical definitions of sensitivity and
specificity are given. Both limits are testable from
first principles, i.e., from measurable pieces of
spectroscopic data. Applying the limits post factum to
today's "statistical" calibration practice reveals why
many PLS/PCR results are affected by unspecific
correlations (which, unlike spurious correlations, do not
disappear when applying PLS or PCR to larger and larger
calibration data sets). An overhaul of practices is
required.
The importance of applying spectroscopic expertise and
application knowledge to the calibration is stressed, as
is the need to scientifically estimate both the "spectral
signal" and the "spectral noise" parts required in
calibration. Both estimates are important because proof
of specificity is a two-step process. First, the user
must prove that the multivariate measurement measures
"the right thing;" and then, second, that this "correct"
measurement is not affected by any unspecific
correlations. Current practices of testing for
specificity (ASTM 1655 etc.) are shown to be insufficient
and misleading in the case of PLS/PCR
| Original language | English |
|---|---|
| Publication status | Published - 2008 |
| MoE publication type | Not Eligible |
| Event | 1st European Conference on Process Analytics and Control Technology, EuroPACT 2008 - Frankfurt am Main, Germany Duration: 22 Apr 2008 → 25 Apr 2008 |
Conference
| Conference | 1st European Conference on Process Analytics and Control Technology, EuroPACT 2008 |
|---|---|
| Country | Germany |
| City | Frankfurt am Main |
| Period | 22/04/08 → 25/04/08 |
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Cite this
Marbach, R., & Teppola, P. (2008). Exact definition of "Specificity of Response" in the multivariate case: Severe consequences for today's practice of PLS/PCR. Paper presented at 1st European Conference on Process Analytics and Control Technology, EuroPACT 2008, Frankfurt am Main, Germany.