Should you “sell in May and go away,” as the old investing adage says? Charles Schwab Chief Investment Strategist Liz Ann Sonders says not so fast.

In commentary on Schwab’s site, Sonders says that it’s true that the market has historically performed better during November-April period than it has during the May-October period. From May 1 through October 31 each year since 1950, the S&P 500 has returned an average of 1.2%, she says, citing data from Ned Davis research. In contrast, the average performance from November 1 through April 30 each year since 1950 was 7.0%.

But, Sonders adds, three of the months in that May-October period (June, July, and August) have historically been among the market’s top performers. In fact, it’s mostly been one month — September — that has historically been dragging that May-October period down.

“All of the seasons seem to be adequately represented [among both “hot” and “cold” months],” Sonders says. “And what we know for a fact is that time horizons have become much shorter over the recent years, and the reaction function gets triggered more often. It’s likely that many investors may find their patience tested when experiencing either a great month (or two) during the May-October ‘all out’ period and/or a poor month (or two) during the November-April ‘all in’ period. Of course, the seasonal trading strategy must consider transaction costs and tax implications.”

Sonders also looks at how particular sectors have fared during different times of year, and how the “Sell in May” mantra has worked out in Presidential election years.

And, Sonders offers a lengthy list of positives that she thinks are reasons why the May-October period won’t be a weak one this year. Among them:

• Inflation is coming down, especially among commodity prices.
• Credit growth is quite strong, especially for consumers.
• Housing has improved markedly.

Sonders thinks the current correction isn’t over, but she does think it could be kept in the normal 5% to 10% range. Sonders also discusses how she thinks the “fiscal cliff” the U.S. is facing in 2013 is having more of an impact than many realize on market and economic psychology.