  We use published spectroscopic and photometric data for 8 Type Ia supernovae
to construct a dispersion spectrum for this class of object, showing their
diversity over the wavelength range 3700A to 7100A. We find that the B and V
bands are the spectral regions with the least dispersion, while the U band
below 4100A is more diverse. Some spectral features such as the Si line at
6150A are also highly diverse. We then construct two objective measures of
'peculiarity' by (i) using the deviation of individual objects from the average
SN Ia spectrum compared to the typical dispersion and (ii) applying principle
component analysis. We demonstrate these methods on several SNe Ia that have
previously been classified as peculiar.
