The nation's largest pension fund on Monday changed its policy on investing in real estate to balance its socially responsible investment philosophy with its quest for profits... [Its] real estate portfolio [lost] nearly half of its value from September 2008 to September 2009... Some of the biggest losses came from investments in real estate ventures whose financial success depended on pushing low-income residents out of rent-controlled housing. The revised policy, adopted at a CalPERS board meeting Monday, says the fund will not participate in investment strategies that rely on eliminating rent-regulated housing or raising rents above regulated levels... California State Teachers' Retirement System [CalSTRS]...is also considering a policy that would ban investments in strategies that are intended to capitalize on displacement of low-income households, spokesman Ricardo Duran said... [refers to Page Mill Properties]