Japan will remain particularly vulnerable to any external shock from America or China while deflation persists.

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One problem with a single currency is that an external shock can hit some countries or regions harder than others.

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If found, such bottlenecks would indicate an external shock to the ecosystem.

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The more rigid wages are, the greater the need for a flexible exchange rate to help the economy respond to an external shock.

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And so market conditions are exerting themselves and that external shock that could always happen in oil, the dog that could bark, it hasn't been barking of late.

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An external shock in the shape of higher oil prices also adversely affected companies exposed to fuel costs during the early stages of 2011, as a crisis in Egypt put pressure on oil prices.

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Historically, it has taken some form of external shock or pressure from overseas, known as gaiatsu, to induce rapid and profound change in Japan (as a result of the 1970s oil shock, for example, Japan started liberalising its finance industry).

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So if the currently rude health of the Indonesian economy were to deteriorate because of policy mistakes or an external shock, the response might be more, not less, liberalisation a swifter dismantling of monopolies, privatisation of the still bloated state sector, and a freer trade regime.

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But the real heart of the optimal currency idea is will the economies react asymmetrically to an external economic shock?

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The automated external defibrillator is a portable, self-contained machine that can shock the heart back into rhythm.

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