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In monetary economics, a money multiplier is one of various closely related ratios of commercial bank money to central bank money under a fractional-reserve banking system. Most often, it measures the ''maximum'' amount of commercial bank money that can be created by a given unit of central bank money. That is, in a fractional-reserve banking system, the total amount of loans that commercial banks are allowed to extend (the commercial bank money that they can legally create) is a multiple of reserves; this multiple is the reciprocal of the reserve ratio, and it is an economic multiplier. Although the money multiplier concept is a traditional portrayal of fractional reserve banking it has been criticized as being misleading. The Bank of England and the Standard & Poor's rating agency (amongst others) have issued detailed refutations of the concept together with factual descriptions of banking operations. 〔http://www.bankofengland.co.uk/publications/Documents/quarterlybulletin/2014/qb14q1prereleasemoneycreation.pdf〕 〔 http://ommekeer-nederland.nl/documents/standard-poors-rating-services-lending-creating-deposits.pdf 〕 Several countries (such as Canada, the UK, Australia and Sweden) set no legal reserve requirements.〔 http://www.imf.org/external/pubs/ft/wp/2011/wp1136.pdf 〕 Even in those countries that do (such as the USA), the reserve requirement is as a ratio to deposits held, not a ratio to loans that can be extended. 〔 http://www.imf.org/external/pubs/ft/wp/2011/wp1136.pdf 〕 Under the Basel III global regulatory standard, it is the level of bank capital that determines the maximum amount that banks can lend.〔 http://www.bis.org/publ/bcbs189.pdf 〕 Basel III does stipulate a liquidity requirement to cover 30 days net cash outflow expected under a modeled stressed scenario (note this is not a ratio to loans that can be extended) however liquidity coverage does not need to be held as reserves but rather as any high-quality liquid assets 〔 http://www.bis.org/publ/bcbs238.pdf 〕 〔 http://www.bis.org/bcbs/basel3/b3summarytable.pdf 〕 In equations, writing ''M'' for commercial bank money (loans), ''R'' for reserves (central bank money), and ''RR'' for the reserve ratio, the reserve ratio requirement is that the fraction of reserves must be ''at least'' the reserve ratio. Taking the reciprocal, which yields meaning that commercial bank money is ''at most'' reserves times the latter being the multiplier. If banks lend out close to the maximum allowed by their reserves, then the inequality becomes an approximate equality, and commercial bank money is central bank money times the multiplier. If banks instead lend less than the maximum, accumulating excess reserves, then commercial bank money will be ''less'' than central bank money times the theoretical multiplier. In the United States since 1959, banks lent out close to the maximum allowed for the 49-year period from 1959 until August 2008, maintaining a low level of excess reserves, then accumulated significant excess reserves over the period September 2008 through the present (November 2009). Thus, in the first period, commercial bank money was almost exactly central bank money times the multiplier, but this relationship broke down from September 2008. == Definition == The money multiplier is defined in various ways.〔 Most simply, it can be defined either as the statistic of "commercial bank money"/"central bank money", based on the actual observed quantities of various empirical measures of money supply,〔 calls the observed multiplier the "actual money multiplier".〕 such as M2 (broad money) over M0 (base money), or it can be the theoretical "maximum commercial bank money/central bank money" ratio, defined as the reciprocal of the reserve ratio, 〔 The multiplier in the first (statistic) sense fluctuates continuously based on changes in commercial bank money and central bank money (though it is ''at most'' the theoretical multiplier), while the multiplier in the second (legal) sense depends only on the reserve ratio, and thus does not change unless the law changes. For purposes of monetary policy, what is of most interest is the ''predicted impact'' of changes in central bank money on commercial bank money, and in various models of monetary creation, the associated multiple (the ratio of these two changes) is called the money multiplier (associated to that model). For example, if one assumes that people hold a constant fraction of deposits as cash, one may add a "currency drain" variable (currency–deposit ratio), and obtain a multiplier of These concepts are not generally distinguished by different names; if one wishes to distinguish them, one may gloss them by names such as empirical (or observed) multiplier, legal (or theoretical) multiplier, or model multiplier, but these are not standard usages.〔 Similarly, one may distinguish the ''observed'' reserve–deposit ratio from the legal (minimum) reserve ratio, and the ''observed'' currency–deposit ratio from an assumed model one. Note that in this case the reserve–deposit ratio and currency–deposit ratio are ''outputs'' of observations, and fluctuate over time. If one then uses these observed ratios as model parameters (''inputs'') for the predictions of effects of monetary policy and assumes that they remain constant, computing a constant multiplier, the resulting predictions are valid only if these ratios do not in fact change. Sometimes this holds, and sometimes it does not; for example, increases in central bank money may result in increases in commercial bank money – and will, if these ratios (and thus multiplier) stay constant – or may result in increases in excess reserves but little or no change in commercial bank money, in which case the reserve–deposit ratio will grow and the multiplier will fall. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Money multiplier」の詳細全文を読む スポンサード リンク
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