And the regulators invented the Basel system of risk-weighted capital ratios, which stipulates different leverage ratios for different categories of loan, in theory to take account of the riskiness of those loans.
They have to hold a minimum total capital of 8% of risk-weighted assets - that is, capital held to back the loans that they make.
And Nationwide's balance sheet, on paper at least, is stronger than that of any of the big banks, with loss-absorbing core capital equivalent to 12.5% of risk-weighted assets, 2.5 percentage points higher than the banks' capital ratios.
The report also noted that Raymond James Bank's ratio of capital to risk-weighted assets was a healthy 10.2%.
Mr Miles said that the optimal ratio of core tier one equity capital to risk-weighted assets would be 19%.
From a text book perspective, Basel III requires banks to hold 4.5% of common equity, Basel II requires 6% of Tier I capital of risk-weighted assets.
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Along with five others, they had been forced to draw up restructuring plans after falling short of the 8% ratio of capital to risk-weighted assets that is considered the acceptable minimum by international financial regulators (by more than six percentage points in the case of Commercial Bank of Korea).
Basel I focused mainly on credit risk, international banks which were required to hold capital equal to 8% of the risk-weighted assets.
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Two interesting wrinkles to the latest version of these tests: banks get a one-time do over if the Fed rejects their capital plan and a key measure of risk-weighted assets has gotten more stringent.
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Since the new Europe-wide rule to strengthen banks is that they must - by the middle of 2012 - have a minimum of 9% capital on a Basel 2.5 basis relative to their risk-weighted assets, after allowing for the fall in the price of their holdings of the debts of over-indebted eurozone countries, by definition it is the banks in those over-indebted eurozone countries that emerge as weakest.
All businesses are allocated capital and are measured by their risk-weighted return on equity.
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Basel II left the minimum capital requirements at 8% of risk-weighted assets.
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He refused to be drawn on what the final outcome would be, but he did not deny that expectations of banks such as HSBC that they'll be forced to hold what's known as core tier one capital equivalent to around 10% of risk-weighted assets are in the right ballpark - or about 3 percentage points more than the new 7% minimum for all banks.
On average, banks have capital equivalent to nearly 18% of their risk-weighted assets more than double the minimum specified by the Bank for International Settlements.
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