Stock investors be ready: You could see some wild gyrations this month, says MarketWatch columnist Mark Hulbert.

Hulbert looked back at 25 years of data for the Chicago Board Options Exchange Volatility Index (VIX), and his research showed that October is the most volatile month of the year.

Hulbert figured the data might be skewed by the fact that the stock market crashed in October of 1987 and 2008. But even when he left those months out of his survey, “the pattern persists of October having well-above-average volatility,” Hulbert writes.

Editor's Note: See the Disturbing Charts: 50% Unemployment, 90% Stock Market Crash, 100% Inflation

He’s unsure why October is so volatile. After all, September is historically the market’s worst performing month.

Obviously, an explanation for the pattern would increase confidence that it will continue, Hulbert says.

“Still, the pattern is significant at the 95 percent confidence level that statisticians often use to conclude that a pattern is genuine,” he writes.

“So, the judgment of history is that we’re in for a wild ride this month.”

While the VIX index currently points to calm in the market, two lesser-known measurements of volatility indicate increasing fear among institutional investors, Jason Goepfert, president of SentimenTrader.com, writes in a report obtained by Reuters.

Both the Credit Suisse Fear Barometer Index and the CBOE S&P 500 Skew Index recently hit or approached record highs.

"When that happens, stocks pull back," Goepfert says.

Editor's Note: See the Disturbing Charts: 50% Unemployment, 90% Stock Market Crash, 100% Inflation