He is the author of the much-celebrated Stocks for the Long Run.

He has long advocated on behalf of stock market investing.

And yes, even in the midst of The Great Recession, Jeremy Siegel still believes that stocks are the best investment for the long run.

When Siegel, Wharton’s Russell E. Palmer Professor of Finance, spoke to Wharton alumni on Saturday morning as part of the School’s 2010 Reunion Weekend,  his message was simple and clear: Stocks are still the answer.

“Stocks are indeed the most volatile short-run asset class,” Siegel said. “But that [volatility] seems to fade into insignificance when you look at the upward thrust in value over time. In the long run, there is no asset class that yields a more stable return. Stocks are the most unstable asset class in the short run and the most stable in the long run.”

History bears that out, Siegel said.

As he told his audience, from 1802 until 2009, the average real return on stocks was 6.6 percent per year, after inflation. Bonds returned 3.6 percent. Bills returned 2.8 percent. And gold? A measly 0.5 percent.

“Over all long-term periods, stocks have returned between 6 and 7 percent per year after inflation,” Siegel said. “It’s quite remarkable. No other asset class even approaches that stability.”

He added: “People talk about the safety there is in government bonds. In the long run, there is no safety in government bonds. I don’t mean default. I mean inflation.”

The value of stocks is not limited to the United States, either. After Siegel published Stocks for the Long Run, a team of British researchers used similar methodology to study returns in more than 16 other countries. The results? Stocks vastly outperformed other asset classes there as well.

“Over the last 100 or 110 years, the U.S. isn’t even No. 1 [in stock market returns],” Siegel said. “South Africa and Australia have higher real returns over the last 110 years than the United States. In every country in the world, stocks have dominated [other] assets. And stocks have dominated them by a large margin.”