"It is very difficult to say if the optimism out there is warranted," Alec Young, global equity strategist at S&P Equity Research in New York, told Reuters. "We don't know what's going on behind the scenes, and that makes it very difficult to account for all the uncertainty out there."
In afternoon trading in New York, the Dow Jones Industrial Average gained 0.11 per cent and the Standard & Poor's 500 Index rose 0.09 per cent. The Nasdaq Composite Index slipped 0.14 per cent.
The latest data showed that the US economy expanded 3.1 per cent in the third quarter-stronger than previously estimated, and that existing home sales rose a better-than-expected 5.9 per cent in November.
However, the number of Americans filing new claims for jobless benefits climbed more than predicted in the latest week.
"It is great to see this kind of growth, but investors know it could all disappear if there's no deal on the cliff," Todd Schoenberger, managing partner at LandColt Capital in New York, told Reuters. "Macro data may be on the back burner for a while."
In Europe, the Stoxx 600 Index closed with a gain of almost 0.1 per cent for the day. Shares in Frankfurt and Paris eked out an advance of nearly 0.1 per cent, while those in the UK slipped by a similar narrow margin.
UK retail sales unexpectedly shrank in November, raising concerns the nation's economic outlook is darkening.
"The economic outlook has got worse and consumers are probably still really uncertain," Rob Wood, an economist at Berenberg Bank in London and a former Bank of England official, told Bloomberg. "There's no good news ahead for them in the near term."