... firstapproximation, the variation in the value of a bonds portfolio can be taken as the response of the value of a bond with the average maturity of the portfolio. For instance, if the average maturity of the ... available.ECB Working Paper No 40 l November 200015Finally, the indicators of the rigidity of bank funding costs are all significant. As expected, the higher the staff costs, the smaller the impact of ... increase in the federal funds rate. In such circumstances, the drop in the value of the bond portfolio will reflect the overshoot of the long-term rate over the MMR.ECB Working Paper No 40 l November...