(Portland, OR)  --  A new report says home values in Portland have risen at the fastest rate in the nation over the past year.  Online real-estate research firm Zillow says the average home in Portland increased in value by 14-point-six percent since September 2015.  That's compared to the nationwide average of five-point-five percent.  Zillow says the increases have been driven by higher demand and a shortage of homes for sale.