Investing when down 50% from the past peak

I was intrigued by Jeremy Siegel's latest comment in Knowledge@Wharton that "once the market has fallen 50% your future returns are even better". So I went back to the data (monthly S&P500 close going back to Jan 1950) and found out that:

(1) Prior to the current crash and using month end data since Jan 50 the S&P 500 never had dropped by 50%.
(2) I therefore looked at 1year, 3 year, 5year and 10 year performances post a drop from the past peak of 40%. Since 1950 only nine months have been 40% below the past peak. It has then indeed paid off to invest as the following tables illustrates. Interestingly no negative performances were registered so far (see note below). It seems hence to be a rare and relatively safe opportunity.

-40% from Peak	1 YEAR	3YEAR	5YEAR	10YEAR
Average	29%	46%	65%	146%
Min	19%	36%	52%	134%
Max	36%	53%	87%	161%
St Dev	6%	7%	11%	14%
All periods
Average	9%	28%	51%	125%
Min	-45%	-43%	-36%	-41%
Max	53%	120%	220%	371%
St Dev	20%	30%	48%	88%

Note that the jury on the 10 year performance following the 2000-2002 bear market is still out though it is not looking too good.

The table above compares the performances following the few occurences when the maket had dropped 40% to the average performances of all 1, 3, 5 and 10 year periods since Jan 1950.

Will have to look further using Shiller's data and real returns.