American economist Robert Shiller of the Case-Shiller Home Price Index of home prices in 20 metro cities across the United States indicated on May 31, 2011 that a "Home Price Double Dip [is] Confirmed"[7] and British magazine The Economist, argue that housing market indicators can be used to identify real estate bubbles. Some[who?] argue further that governments and central banks can and should take action to prevent bubbles from forming, or to deflate existing bubbles.