As reported here, quoting Paul Dales, senior economist at Capital Economics:
“On the Case-Shiller measure, prices are now 33% below the 2006 peak and are back at a level last seen in the third quarter of 2002. This means that prices have now fallen by more than the 31% decline endured during the Great Depression.”
The article concludes that it is probably even worse than that, if current modest inflation is factored in compared to the deflation prevalent in the 1930s.