Choosing the hedge: capped vs two-sided
A futures hedge neutralizes both sides — upside and downside go together. A purchased option caps the loss at the premium and keeps upside open: it is insurance, not a risk exchange. Selling options earns premium but accepts a fat downside tail; as a hedge it makes sense mainly inside structures (a collar: buy put, sell call) that trade capped upside for cheaper protection. The right choice starts from the loss profile of the real exposure, not from instrument prices.
- Two-sided risk, full removal → futures/forwards sized by minimum-variance ratio.
- Protect from loss, keep upside → purchased put/call (insurance with a known premium).
- Premium too rich → collar or spread (accept capped upside).
- Contractual rate risk → IRS or caps/floors on the reference rate.
Measurement: VaR, CVaR and stress testing
VaR at confidence α over horizon h is a single number: the loss not exceeded with probability 1−α. Three routes: historical (empirical distribution), parametric (normal/lognormal with variance-covariance) and Monte Carlo. VaR's structural weaknesses: it says nothing about the tail beyond the cut, and it is not additive. CVaR — the mean loss in the worst 1−α — fixes both to a large degree and is coherent under distribution shape. Stress testing inverts the question: 'if this scenario happens, what is the loss?' — and because you build the scenarios, it sees what VaR cannot by definition.
Worked example: parametric VaR on a 10m portfolio
- V = $10,000,000; annual vol σ = 18%; horizon 10 days; α = 99% → z = 2.33.
- Horizon vol: σ_h = 0.18 × √(10/252) = 3.58%.
- VaR = 2.33 × 0.0358 × 10M ≈ $835,000.
- Interpretation: in normal conditions, 10-day losses exceed ~$835k with 1% probability — it is not a worst-case loss.
نتیجه: VaR is probabilistic and conditional; in real crises (correlation breakdown, fat tails) losses can be multiples of it. That is why institutional practice pairs VaR with CVaR and stress testing.
No metric is a 'maximum possible loss'. Tail events, correlation breakdowns and regime shifts outrun every linear, normal model. Metrics are maps, not walls — position sizes must survive leaving the map.