FRESH PERSPECTIVES
unknown sample is predicted as belonging to the group from this model, there is still some uncertainty. On the other hand, there is a very high degree of certainty in a sample being predicted as an active at this stage.
Classes for modeling – NP1 and NP2 placebos (I); actives(II) Classes excluded: tablet and capsule placebos all actives
Figure 14 - Class predicted probability – PLSDA model with NP1
/NP2
Last tier model – NP1
/NP2
placebos vs. NP2
active
A sample that makes it to the third tier model that is designated as a placebo could actually be an active of NP2
/NP2 placebo and NP2 cm-1 and 1615 cm-1 . Figure 15 provides some insight
as to why this might be the case. The only signifi cant diff erence between the NP1
active classes are very minor features at 1506 . Adding a fourth tier model that diff erentiates between placebos and NP2
Figure 16 - Class predicted probabilities - PLSDA model with NP1
actives /NP2 placebos and
placebo class
Figure 15 - Comparison of mean spectra of NP2
active class and the NP1 /NP2
Figure 17 - Flowchart for fi nal hierarchical model to classify placebos and actives
66 American Pharmaceutical Review | Fresh Perspectives 2013
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