So at what point did the 2nd derivitive turn positive during that timeperiod 1980-20010? When did it max out? When did it turn negative (if at all)?[/quote]
1998 appears to be the year San Diego rents really diverged from the US as a whole. Between 1998 and 2005 San Diego rents increased by 6.3% annually versus 3.4% for the US. Since 2005, both series have increased by about the same amount.
