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By combining the newly infrared photometric data from the All-Sky DataRelease of the Wide-field Infrared Survey Explorer with the spectroscopic datafrom the Seventh Data Release of the Sloan Digital Sky Survey, we study thecovering factor of warm dust ($\CF$) for a large quasar sample, as well as therelations between $\CF$ and other physical parameters of quasars. We find astrong correlation between the flux ratio of mid-infrared to near-ultravioletand the slope of near-ultraviolet spectra, which is interpreted as the dustextinction effect. After correcting for the dust extinction utilizing the abovecorrelation, we examine the relations between $\CF$ and AGN properties:bolometric luminosity ($\Lbol$), black hole mass ($\MBH$) and Eddington ratio($L/L_{\rm Edd}$). We confirm the anti-correlation between $\CF$ and $\Lbol$.Further we find that $\CF$ is anti-correlated with $\MBH$, but is independentof $L/L_{\rm Edd}$. Radio-loud quasars are found to follow the samecorrelations as for radio-quiet quasars. Monte Carlo simulations show that theanisotropy of UV-optical continuum of the accretion disc can significantlyaffect, but is less likely to dominate the $\CF$--$\Lbol$ correlation.

The Covering Factor of Warm Dust in Quasars: View from WISE All-Sky Data Release