U.S. angel investors continued to shy away from funding start-ups at the idea or concept stage in 2010, according data released Tuesday by the University of New Hampshire’s Center for Venture Research.

About 31 percent of angel investors gave seed or early stage capital last year, a decline of 4 percent compared to 2009, the center said.

But Jeffrey Sohl, the center’s director, said he believes a “cautious optimism to investing is taking hold.” Angel investments improved during the second half of the year, according to the center’s latest data.

Overall angel investment increased 14 percent to $20.1 billion last year, compared to 2009. The number of investors was 265,400 people, a 2 percent increase from 2009.

Whether the investment dollars will come to Minnesota start-ups at the idea or concept stage remains uncertain. Several Minnesota angel investors said part of the problem is they aren’t getting rewarded enough for the risk in investing in unproven business ideas.