To begin with, the VaR estimate is founded on precedent data, that is, it uses past distribution of effects of the investment. However, to calculate the peril of an investment, it is of no concern how big this risk has been in the earlier period, but fairly on how much exposure there is within the existing period; therefore, the future distribution of outputs would be the appropriate to consider. As long as the division of outcomes stays steady, the VaR can simply be removed from the past distribution. In reality, the distributions are not steady over time; most remarkably, the inconsistency of outcomes and the correlations vary. Relying exclusively on past data can as a result give a poor risk measure Oldfield, et al (2000).
Unluckily, even with this problem resolved, there lingers an issue with the evaluation of the VaR itself. Since the true probability circulation is not well known in general, it has