Mebane Faber of Cambria Investment Management provides this useful chart from The Leuthold Group. It shows the average length and depth of bear markets going back to 1899. The data shows the following:
Average bear market decline (1899-2009): -37%
Average bear market decline (1945-2009): -30%
2011 bear market decline: -19%
By historical standards, this bear market remains meager.