The S&P 500 has been stuck in a narrow range this year, trading between 3,800 and 4,200. After recently climbing towards the top of that range, the index fell last week, disappointing bulls who were hoping for an upside breakout.

Nevertheless, Bespoke Investment data suggests stocks are now in a clear uptrend. Even as stocks rebounded strongly at last October’s market bottom, the S&P 500′s 200-day moving average continued to slope downward, hitting a new 52-week low in March. The 200-day moving average, which tracks the average price over the previous 200 days, however, is now rising again.

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Bespoke found 20 previous instances where the index’s 200-day moving average rallied after hitting a 52-week low. A year later, stocks were higher every single time, averaging gains of 18.2 per cent. An index’s 200-day moving average has a “slow-moving nature”, says Bespoke. “Like a cruise ship,” it “doesn’t just turn on a dime so when it starts to shift directions, it’s usually a reflection of the fact that the market’s longer-term trend has shifted”.