The S&P 500 Index has roughly doubled from its credit-crisis low, but many small investors haven’t bought into the historic rally in U.S. stocks.

The S&P 500 is known as a barometer of U.S. economic health. The index has rallied about 97% and pulled stock exchange traded funds (ETFs) higher even though many investors remain worried about the economy and job market.

Still, S&P 500 earnings are poised to surpass the 2007 peak of $90 a share in the third quarter after surging from $7 in March 2009, says Rita Nazareth and Michael Patterson for Bloomberg. Recent data indicate that the gap between projected 12-month profits and average earnings over the last 10 years is set to widen the most since 1951.

Some anticipate that the investors who have sat on the sidelines thus far will help advance the index further with future purchases, even while earnings may become sluggish later this year. Thus far, retail investors took money out and hedge funds have plowed in, reflecting the low confidence that individual investors have been plagued with. [How To Play The S&P 500 With ETFs.]