If the insatiable demand for bonds has upended the models youuse to value them, you're not alone.

Just last month, researchers at the Federal Reserve Bank of NewYork retooled a gauge of relative yields on Treasuries, castingaside three decades of data that incorporated estimates for marketrates from professional forecasters. Priya Misra, the head of U.S.rates strategy at Bank of America Corp., says a risk metric she'srelied on hasn't worked since March.

After unprecedented stimulus by the Fed and other central banksmade many traditional models useless, investors and analysts alikeare having to reshape their understanding of cheap and expensive asthe global market for bonds balloons to $100 trillion. With theworld's biggest economies struggling to grow and inflation nowherein sight, catch phrases such as “new neutral” and “no normal” aregaining currency to describe a reality where bonds are rallying themost in a decade.