Mr Miles said that the optimal ratio of core tier one equity capital to risk-weighted assets would be 19%.

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Requiring banks to maintain a ratio of 10 percent of equity capital to total assets would make them less likely to need a government bailout in the next financial crisis.

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The Vickers Commission, set up the chancellor, recommended that there should be a ratio of 4.06% of pure equity capital to gross loans and investments, as what is known as a "backstop leverage cap", for the biggest banks.

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It's yielding 4.8% and has a fortresslike tangible equity ratio (capital minus intangible assets) of 13.9%.

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Its ratio of assets (loans and investments) to loss-absorbing equity capital is a fraction over 20 times, down from 50 times in the autumn of 2008, when it was rescued from the brink by taxpayers.

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If a buyback raises the debt-to-equity ratio, it can lower the firm's overall cost of capital (because in most countries interest payments, unlike dividends, are tax deductible).

ECONOMIST: Share nonsense

Ssangyong Oil Refining, the biggest shareholder in Ssangyong Motor, boasts shareholders' equity of 1.1 trillion won and a capital-reserve ratio of 385%.

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"With its high leverage ratio to tangible common equity, we believe Lehman needs to raise substantial capital regardless of market conditions in order to take its needed write-downs, " Einhorn said in an email Tuesday.

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