3. If the marginal distributions are unimodal and symmetrical, it may be
useful to assume Gaussian statistics (multivariate normal pdfs).
4. A nonlinear transformation can make a feature’s pdf symmetrical.
5. A multimodal pdf suggests the presence of subclasses. Judicious use of
subclassing and feature transformations can often make the Gaussian
assumption work.
6. When a particular functional form for the pdf (the Gaussian, for ex-
ample) is known, less training data is required since it is used only to
estimate the parameters. This gives rise to a parametric classifier.
7. If the functional form of the pdf is not given or it is known to be non-
Gaussian, one must estimate the pdfs directly from the training data.
Such classifiers are nonparametric,