在asset allocation part 1中的第133页ppt中，有一句话“the observed relationship that the allocation to corporate bonds declines with increasing surplus return can be explained by the positive correlation of bond price with the present value of liabilities." 为什么corporate bond和liability的相关性会更强呢？多投corporate bond，图中显示风险会下降。那么不是应该相关性更弱，甚至于负相关，才会分散化效果更强吗？
