Both these techniques might be infeasible to use when the environment is so unstable that neither past experience nor expert judgment will provide a reliable base of information.  Both may be feasible when there is some instability in the environment. Statistical information could be examined in comparison to leading indicators.  This might help define a relationship between actual changes in the environment and what happens to human resources.  For example, in a bank, although mortgage interest rates may be unstable, there is a strong, negative correlation between mortgage interest rates and the number of analysts necessary to process mortgage applications Judgment of experts may be needed, however, to attempt a projection of what may happen to mortgage interest rates in the future.