  The well-documented E1 relationships are first extended to infrared color
$\alpha(60,25)$ and flux ratio [OIII]/H$\beta_{\rm{n}}$ by comparing emission
line properties to continuum properties in infrared wavelength. Both direct
correlations and a principle component analysis are used in a sample of 50 IRAS
IR-selected Seyfert 1.5 galaxies. In addition to confirm the correlations of E1
in Boroson & Green (1992), our Eigenvector 1 turns out to be dominated by
mid-infrared color $\alpha$(60,25), and most strongly effected by RFe,
[OIII]/H$\beta_{\rm{n}}$, and EW(H$\beta_{\rm{b}}$). Our analysis indicate that
the objects with large E1 tend to co-existent with relatively young nuclear
stellar populations, which implies that the E1 is related with nuclear
starformation history. The IR-dominated Eigenvector 1 can be, therefore,
inferred to be interpreted as ``age'' of AGN. In confirmation of Xu et al.
(2003), it is clear that the extreme Seyfert galaxies with both large RFe and
large [OIII]/H$\beta_{\rm{n}}$ are rare in our Universe.
