Some visuals from UBS research:
Identifying a bubble: Price bubbles are a recurring phenomenon in property markets. The term “bubble” refers to a substantial and sustained mispricing of an asset, the existence of which cannot be proved unless it bursts. But historical data reveals patterns of property market excesses. Typical signs include a decoupling of prices from local incomes and rents, and imbalances in the real economy, such as excessive lending and construction activity. The UBS Global Real Estate Bubble Index gauges the risk of a property bubble on the basis of such patterns. The index does not predict whether and when a correction will set in. A change in macroeconomic momentum, a shift in investor sentiment, or a major supply increase could trigger a decline in house prices.
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