Bitcoin has been characterized as a speculative bubble by eight winners of the Nobel Memorial Prize in Economic Sciences: Paul Krugman,[92] Robert J. Shiller,[93] Joseph Stiglitz,[94] Richard Thaler,[95] James Heckman,[96] Thomas Sargent,[96] Angus Deaton,[96] and Oliver Hart;[96] and by central bank officials including Alan Greenspan,[97] Agustín Carstens,[98] Vítor Constâncio,[99] and Nout Wellink.[100]