To establish the VaR number of the portfolio for a given level of confidence the
standard deviation must be multiplied by the relevant scaling factor, which is
derived from the standard normal distribution. For example, if a 99 per cent level of
confidence is desired the appropriate scaling factor is 2.33 since the probability of
occurrence of a number less than -2.33 is 1 per cent. Scaling the standard deviation
of the portfolio by this amount yields a VaR number which should only be exceeded
1 per cent of the time. Note that the choice of a 99 per cent confidence level and
associated scaling factor of 2.33 assumes a one-tailed test in line with the Basle
market risk requirements (that is, only large losses are considered, not large profits).