Professor Robert Shiller: "The aggregate economy is at a turning point and there is much uncertainty now."

According to Robert Shiller, professor of economics at Yale University and co-founder of the S&P/Case-Shiller Home Prices Indices, the aggregate economy is "at a turning point and there is much uncertainty now."

Shiller made the comment during a live chat was hosted by S&P Indices on S&P's online site, and was timed with the 9 a.m  EST, July 26th release of the May results for the S&P/Case-Shiller Home Price Indices, a measure of single-family residential home prices in the United States.

The May reading of the Case/Shiller Home Price Index posted at -4.51% on a year-over-year basis. Expectations had been for -4.50% year-over-year.

During the chat, Shiller estimated that seasonal factors are growing stronger and may reflect anomalies of the financial crisis. He said seasonality is hard to judge at the current time.

Shiller said the most important metric to watch right now is the recent trend in home prices. Next important would be jobs, and after that survey measures of home buyer confidence, he said.

Shiller noted that the home buyer tax credit expired in early 2010,  and that home prices resumed their downward trend after support was withdrawn.

See the entire chat, which included comments from David Blitzer, managing director and chairman of the index committee at S&P Indices, here.