A new study co-authored by Yale School of Management finance professor James Choi has found that there is no longer a correlation between a mutual fund’s past and future performance. This according to an article in Yale Insights.

As part of the study, Choi and finance doctoral student Kevin Zhao replicated a 1997 analysis by Mark Carhart that tracked mutual fund performance between 1963 and 1993, then extended the analysis to present day. The team found that from 1994 to 2018, a fund’s performance is completely unpredictive of its future returns. The article says, “even in the period that Carhart examined, a statistically significant correlation was only seen in the years before 1980.”

According to Choi, this shift has occurred because momentum—the tendency for stocks that yielded high returns in the past year to do well in the following year—was a bigger contributor years ago, but has weakened in recent years. Choi says, “Even if you happened to be holding high-momentum stocks in your portfolio, that didn’t give you as much of a return going forward as it used to.” Further, high-performing funds tend to hold less of their portfolios in high-momentum stocks. Choi explains that “funds aren’t doing as much of a good thing as they used to, and the good thing isn’t as helpful as it used to be.”

Choi asserts that the study “adds weight to the idea of choosing a passive strategy rather than an active fund that’s trying to beat the market.” He also says the findings underscore the importance of challenging older research findings: “Financial markets and economies aren’t like physics, where in any kind of human scale of time, the laws and phenomena are all the same. People and societies change, and markets change, so it’s important to periodically re-check facts that we presume to be true. There’s no law that says they have to be true forever.”