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With just one trading session left, September is on track to be one of the least volatile on record, according to LPL Research.

The range between the S&P 500 Index's day-to-day session highs and session lows has only been 0.39%, which is the smallest average range during September since at least 1970 when reliable single-day data became available, LPL wrote in a blog post on Wednesday, Sept. 27.

Last week, the S&P 500 marked 41 consecutive weeks without a weekly move greater than 2% in either direction, LPL found. The only times with longer streaks were in the mid-1960s and mid-1990s, which rank as two of the least volatile periods in history.

The CBOE Volatility Index undefined , which measures volatility in the stock market and is often referred to as the "fear index," was down nearly 3% on Thursday, Sept. 28. In the last month, the index has fallen more than 15%.

While September has been quiet, LPL said it expects the fourth quarter to heat up with volatility taking a turn higher. October is known to be one of the most volatile months of the year. Since 1970, LPL wrote, no month has had more 1% changes either higher or lower, and nearly 30% of all October trading sessions closed up or down at least 1%.

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