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longer - term refinancing operations ( ltros ) and decides the main refinancing operations to be carried out through a fixed - rate tender procedure with full allotment. ecb cuts the base interest rate from 2. 50 % to 1. 00 %, and introduces the first covered bond purchase programme ( cbpp1 ). ecb activates the securities markets programme ( smp ). the ecb launches the second covered bond purchase programme ( cbpp2 ) and introduces the 3 - year ltros. the ecb announces the outright monetary transactions ( omts ). the ecb cuts the base interest rate to 0. 25 % and introduces forward guidance. the ecb cuts the base interest rate to 0. 05 % and the deposit facility rate to - 0. 20 %, bringing it for the first time in negative territory and introduces the targeted longerterm refinancing operations ( tltro ) with a 4 - year maturity. ecb introduces the expanded asset purchase programme ( app ) and cuts the deposit facility rate to - 0. 30 %. ecb accelerates the expanded asset purchase programme ( app ) and cuts the main refinancing operations ( mro ) rate to 0. 00 % and the deposit facility rate to - 0. 40 %. indeed, the 10 largest central banks now own assets totaling $ 21. 4 trillion, accounting for 29 % of the world economy, up by 10 % from end - 2015, double what it was in midseptember 2008 and almost half the value of all debt in bloomberg ’ s global bond index ( as shown in chart 1 )! chart 1. the combined assets of the 10 largest central banks finally, almost 75 % of the world ’ s central bank assets are controlled by policy - makers in four regions : china, the us, japan and the eurozone. the following six – that is, the central banks of england, brazil, switzerland, saudi arabia, india and russia – each account for an average of 2. 5 %. the remaining 107 central banks tracked by bloomberg, mostly with imf data, hold less than 13 % ( see chart 2 ). chart 2. central banks ’ combined assets chart 3. stock of assets purchased by the four major central banks as a percentage of national gdp source : bank of greece, european central bank, fed, bank of england and bank of japan. note : the ecb ’ s purchased assets in the context of the