Gregg Fisher is waiting for the stock market to right itself after a decade of standing on its head.

As of fall, Fisher notes that the equity market has endured 10 straight years where large-cap growth, meaning larger and more expensive companies, tended to outperform small-cap value, or smaller and less-pricey businesses.

In a recent paper, Fisher, founder and head of quantitative research and portfolio strategy at New York-based Gerstein Fisher, asks why the small and value factors, which in the past have offered investors enhanced equity returns, seem to have lost their effectiveness, and wonders if they will ever return to their benchmark-beating ways.

“[Size and value] are arguably the two most important, longest-standing and heavily researched investing factors,” says Fisher. “It’s been a good 10 years for these companies that are huge and super expensive, but maybe that alone is reason to consider exposures to things that haven’t gone up that much.”

Value investing, originally conceived by Ben Graham and David Dodd as careful financial analysis that precedes an investment decision, still cleaves to the principle that higher returns can be generated through investing in stocks with lower valuations. Today, investors of all stripes can access at least some of the value premium by purchasing passive funds based on the cheapest segment of stocks selected from a benchmark index like the Russell 1000 or the S&P 500.

Small-cap investing, as described in the 1980s, links higher returns to the size of the company, with lower market capitzliation companies historically offering higher returns.

Fisher found that from 1927 to the end of September, small-cap value stocks have outperformed large-cap growth stocks by an annualized 5 percent or more. As investors are exposed to higher concentrations of smaller or less valuable stocks, their historical returns increase incrementally.

Since 2007, large-cap growth investing has outperformed small-cap value investing by nearly 3 percent per year, and both small-cap and value investing strategies have tended to lag core indexes like the S&P 500, says Fisher.

Fisher wonders if the last 10 years represents an aberration rather than a long-term trend, noting that 10-year investment periods tend to be idiosyncratic and not necessarily indicative of future market performance. Even 20-year investment periods can be idiosyncratic, says Fisher, who noted that in February 2009, the equity market premium, or the performance associated with investing in stocks versus low-risk bonds, had turned negative for the trailing 20 years, meaning the risk-free rate of return exceeded the returns provided by equity markets between February 1989 and February 2009.

“For the past 20 years, there had been no reward for risk. That happened to be a moment where bonds did better than stocks and the risk premium on equities was at its most negative point ever,” says Fisher. “As it turns out, that would have been the worst period of time ever to have gotten out of the stock market. I would say we’re in a similar period of time for value versus growth or small versus big.”

Fisher looked across 1,000 different rolling 10-year periods over the last 90 years, noting that small-cap value strategies still outperform large-cap growth 87 percent of the time, but the return premium for the size and value factors is cyclical over time and depends on the market environment.

Over the past two decades, the annualized 10-year, small-cap value premium swung between positive 15 percent and negative 5 percent, according to Fisher, which means that the factors are most likely currently in a temporary stretch of negativity.

“Empiricaly, this would appear to be a reversion to the mean story. We’re in the 13 percent of the time that small-cap value deosn’t do better,” says Fisher.

Fisher found that investor patience is key to making the size and value factors work: The longer the time period studied, the more likely small-cap and value strategies outperform. Based on nine decades of market data, tilting a stock portfolio towards smaller capitalization and less expensive stocks over the longest possible timeframe still produces significant outperformance.

Fisher also asked whether a different market scenario could “break” factor cyclicality, noting that “historical data alone isn’t enough to build an investment strategy.” In recent years, some market strategists have suggested that the rise of passive and hands-off investing in market-capitalization weighted index funds is distorting the market and breaking the link between risk and return.

“The popularity of indexing might be programmatically causing the momentum premium in the market to be an even bigger deal,” says Fisher. “Along the way, rising prices attract more capital, which causes prices to rise even further, which attracts still more capital and even higher prices. I think most of us are reasonable enough to understand that that movie has to end at some point in time. Eventually, investors will stand up and say that they don’t think their portfolios should have companies with stocks trading at 500-times earnings.”

Value investing still links perceptions of risk to higher returns, says Fisher. Old, slowly growing industrial firms with high costs must offer higher returns than large, healthy, quickly growing technology firms with higher valuations, or investor capital will avoid the old and flock to the new. Market participants still over- and under-react to headlines, mispricing equities and creating opportunities for value investors, says Fisher. As bull markets age, investor appetite for high valuation stocks increases, opening up more opportunities to access value.

The potential outperformance offered by small-cap investing is also still connected to additional risk, as information about smaller companies still moves more slowly and is accessed by fewer people than information about larger companies. Small companies generally carry smaller cash reserves and conduct less-diversified business operations, making them inherently riskier investments compared to larger companies. Fisher argues that the principles behind small-cap investing still hold.

“Statistically, there really isn’t evidence that the world has changed. Risk and reward are still related,” says Fisher.

Even if value and size strategies render no opportunities for higher returns moving forward, Fisher argues that there’s still a diversification benefit to be had in accessing the strategies and rebalancing between core benchmarks and value- or size-based indexes. When Fisher rebalanced between 25 percent small-value and 75 percent large-growth strategies in a portfolio between July 1, 2012, and June 30, 2017, he produced risk-adjusted returns similar to an all large-cap growth strategy while maintaining some exposure to the size and value factors.

After 10 years of poor results, Fisher says that investors can still make size and value investing work if they’re patient and disciplined.

“Even if the world is different and these premia no longer exist, if big wealthy companies have more prospects than small distressed ones, you should still have exposure to both because none of us really know for sure,” says Fisher.