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Chief executives are less optimistic about the economy this year than last, a survey unveiled at the World Economic Forum suggests.

PwC's annual survey shows that just 37% think the economy will improve in 2015, down from 44% last year.

Perhaps unsurprisingly, Russia's bosses have gone from the most confident to the least, due to problems caused by sanctions and the falling oil price.

In the UK, concern had risen sharply about the availability of talent.

The number of chief executives concerned about the skills gap rose from 64% last year to 84% this year. That is considerably higher than in Germany, France or Spain.

This was partly put down to the high level of employment in the UK, which means that there is a smaller pool of workers to choose from, and partly due to concerns about the education system.

On a global level, the biggest worries that chief executives have are geo-political uncertainties, over-regulation and cyber security.

The report, which was launched at the World Economic Forum, in Davos, said that "concerns about cyber threats have shot up most compared to last year - and in light of the recent attacks on gaming and entertainment networks, the perceived risk will only increase".

Emerging markets

Dennis Nally, chairman of PwC said: "CEO confidence is down notably in oil-producing nations around the world as a result of plummeting crude oil prices. Russia CEOs, for example, were the most confident in last year's survey, but are the least confident this year.

"Confidence has also slipped among CEOs in the Middle East, Venezuela, and Nigeria," he said.

He also pointed out that there appeared to a shift in confidence from emerging market to western markets.

Chief executives ranked the US as their most important market for growth over the next year, putting it ahead of China for the first time in the five years that the question has been asked.

PwC interviewed more than 1,300 chief executives in 77 countries for the survey. It was carried in the final three months of 2014.