Investors hoping to avoid the first annual decline for major U.S. stock indexes since 2015 are dreaming of a Santa Claus rally.

Since 1969, the S&P 500 has averaged a gain of 1.3% over the seven-day period that encompasses the last five sessions of the year and the first two trading days of the new year, according to Dow Jones Market Data.

Such a year-end boost will likely be necessary if the S&P 500 is to avoid finishing in the red. It is down 2.8% this year through Friday.

But trade tensions with China, slumping commodities prices and concerns about the Federal Reserve’s pace of interest-rate increases have forced investors to reassess the global growth outlook.

The Fed is widely expected Wednesday to raise interest rates for a fourth time this year and likely indicate how much and how often officials expect to increase rates in coming years.