Lognormal Var Formula Question
Hello, I’m confused about a very easy question, how to calculate the lognormal Var. Here you are the question and answer:
The annual mean and volatility of a portfolio are 12% and 30%, respectively. The current value of the portfolio
is GBP 2,500,000. How does the 1-year 95% VaR that is calculated using a normal distribution assumption
(normal VaR) compare with the 1-year 95% VaR that is calculated using the lognormal distribution assumption
a. Lognormal VaR is greater than normal VaR by GBP 487,050
b. Lognormal VaR is greater than normal VaR by GBP 787,050
c. Lognormal VaR is less than normal VaR by GBP 487,050
d. Lognormal VaR is less than normal VaR by GBP 787,050
Correct answer: a
Explanation: Normal VaR is calculated as follows:
Normal VaR (%) = Rp – z = 0.12 – (1.645 * 0.3) = 0.3735 = 37.35% (dropping negative sign)
and, Lognormal VaR is calculated as follows:
Lognormal VaR (%) = 0.12 – e[Rp – z] = 0.12 – exp [0.12 – (1.645 * 0.3)] = 0.56832 = 56.83%
Hence, Lognormal VaR is larger than Normal VaR by: 56.83% – 37.35% = 19.48% per year. With a portfolio
of GBP 2,500,000 this translates to VaR = 0.1948 x GBP 2,500,000 = GBP 487,050.
As I understood, the formula should be
Lognormal VaR (%) = 1 – e[Rp – z] , not Rp-– e[Rp – z] (used in this case)
Do you have an explanation please? Thanks for your help
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