This observation, combined with the increased securitization of real estate into diversified national portfolios, gave buyers – and those rating the securitizations – confidence that the “real estate cycle risk” was substantially mitigated through diversification. But, as Figure 7 shows, the assumption that a geographically diversified portfolio of real estate assets would avoid price declines proved wrong. While prices nationally had not experienced a substantial decline in the past, for three years the U.S. has experienced substantial and sustained declines in prices. Some of my colleagues point out, probably appropriately, that given the historical data the failure to anticipate nationwide house prices falling is largely understandable. It was certainly very widespread. What may be more surprising is that in the 2005 timeframe, when many were expecting house prices to slow down or flatten, there was not much by way of risk mitigation undertaken. Myth 2 – Triple-A mortgage securities carried little risk The securitization market – that is, the market for securities based on various slices of pooled mortgages – grew dramatically over the past decade. One reason for the growth in securitization was investor interest in, and demand for, securities with little credit risk but returns above those of Treasuries. Many buyers of such securities felt sure of two things. First, that national real estate prices were quite unlikely to fall – in other words, our Myth 1. Second, that even in the highly unlikely event that the price of a national portfolio did fall, they would be protected by the structure of the securitization.

Securitizations were structured so that any losses were first borne by lower-rated securities built from the pool of underlying mortgages. Given the structure, the assumption was that lower-valued securities would take all potential losses if borrowers defaulted. Many – but not all, of course2 – assumed that home-price declines and related defaults would have to be very extreme before the highest rated, Triple-A securities were impacted. Under this assumption these securities fully deserved the Triple-A rating given by the rating agencies. I should note that making this assumption about Triple-A rated mortgage backed securities (MBSs) proved less problematic than making this assumption about the recombined lower  2  Boston Fed researchers note some examples of contrary analysis of Subprime ABS structures written in 2005 suggesting vulnerability to even a 5 percent fall in house prices. See “Making Sense of the Subprime Crisis” by Paul Willen with Kristopher S. Gerardi, Andreas Lehnert and Shane Sherlund (Brookings Papers on Economic Activity, Fall 2008). BIS central bankers’ speeches  3  tranches of mortgage-backed securities that were billed as Triple-A rated collateralized debt obligations (CDOs).3 But many investors focused not on the security’s underlying components, merely on the ratings. Figure 8 shows that Triple-A securities remained at par values as the securitization boom gathered steam. However, Figure 9 shows that when the severity of the decline in house prices manifested itself, even the Triple-A rated mortgage securities collapsed in value.