Federal Reserve chairman Ben Bernanke has laid out four "unconventional" policy options to boost the US economy.

美联储主席本·伯南克放出四个“非常规”政策以促进美国经济增长。

Mr Bernanke said all of the possible policy options contained risks

Top of the list is more "quantitative¹ easing（量化宽松） " - mass purchases of debt.

Speaking to fellow central bankers at the annual Jackson Hole symposium²（讨论会，座谈会） in Wyoming he said the recovery had slowed to "a pace somewhat weaker" than forecast.

Hours earlier economic growth for April to June was revised to an annualised（年度的） rate of 1.6%, down from 2.4%.

His speech came in the wake of a string of disappointing US economic data in the past month that point to a sharp slowdown in the second half of the year.

Earlier on Friday the US Commerce revised its estimate of second quarter GDP growth down to 1.6%, although this cut was much lower than most Wall Street analysts³ had expected.

It stands in sharp contrast to a small upward revision of UK economic data, and very strong economic growth in Germany.

Unorthodox toolkit

"The issue at this stage is not whether we have the tools to help support economic activity and guard against disinflation（通货紧缩） [a falling rate of inflation]," Mr Bernanke said.

He said the unorthodox（非正统的） policy options each contained risks and would only be used if the outlook worsened further.