The bear market has more room to run, according to Bernstein analyst Ann Larson. So far, the U.S. stock market 's downturn has lasted nine months and there have been four bear market rallies, the firm pointed out in a note Tuesday. While the summer upswing had some wondering if relief was in sight, stocks tumbled on Tuesday, suffering their worst day since June 2020 after inflation numbers came in higher than expected. The S & P 500 , which hit a low of 3,636.87 on June 17, is still down more than 17% year to date. There are three key reasons why there will be more pain ahead, Larson said. To come up with her thesis, she analyzed sell-offs going back 85 years. For one, most major global downturns ended with a moderate inflation/low-growth regime. In addition, return correlations of major global markets with U.S. markets have been increasing, which typically coincide with big market drawdowns. Lastly, hopes for a more accommodative Federal Reserve have been dashed. "Powell's speech at Jackson Hole and the most recent CPI print likely indicate that a Fed pivot is off the table anytime soon, making markets more vulnerable to rate hikes and growth concerns," Larson wrote. Bernstein studied bear markets dating back to 1937. It defined bear markets loosely, with sell-offs between 15% and 20% rather than the traditional 20%, so that it could study more periods. In addition to the average 28% drop, it found that the downturns lasted an average seven months, with an average three bear market rallies. The longest bear market lasted 25 months during the dotcom recession in the early part of the century, and had eight rallies. The shortest downturns were during a recession ignited by the Iran revolution and former Fed Chairman Paul Volcker's inflation fight in the early 1980s, and Covid in 2020, both of which lasted just two months. That said, there are a few reasons to be optimistic, Larson said. If the U.S. is at or near peak inflation, that has historically led to positive S & P 500 returns over a 12-month horizon, she noted. "In addition, current consumer sentiment is at lower levels than we saw even during the global financial crisis, and troughs in consumer sentiment in the past have been buying opportunities one year out," Larson said. However, a recession could complicate matters. Since 1955, the S & P 500 has dropped 13% when leading economic indicators are pointing to a recession, as they are today, she said. Since 2000, that drop has averaged 35%. — CNBC's Michael Bloom contributed reporting.