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FRM Part II · FRM Exam Part II · The Vasicek and Gauss+ Models

A risk manager calibrates a Vasicek model with k = 0.25 per year. Approximately how long is the half-life of a deviation of the expected short rate from θ? Use ln 2 = 0.6931.

The half-life is ln2 divided by k, which is 0.6931/0.25 = 2.77 years. This is the time for the expected gap between the short rate and the long-run mean θ to halve.

  1. A0.69 years
  2. B1.39 years
  3. C2.77 yearsCorrect
  4. D5.54 years

Explanation

The expected deviation decays as e^(−kt). Half-life = ln2/k = 0.6931/0.25 = 2.77 years. Using ln2 alone gives 0.69, and 1.39 results from ln2 × 2 mistakenly, which is not valid.

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