How do historical and hypothetical scenario analyses differ, and how should a risk manager design effective stress tests?

Question

AcadiFi · Accepted Answer

**Scenario analysis** evaluates portfolio performance under specific sets of conditions — either drawn from historical events or constructed from hypothetical narratives. Unlike VaR, which produces a single number from a statistical model, scenario analysis asks **"what if this specific situation occurs?"**

**Two Main Approaches**

| Type | Description | Strengths | Weaknesses |
|---|---|---|---|
| **Historical** | Replay actual market conditions from a past crisis | Realistic, plausible, data available | Past may not repeat; missing novel risk factors |
| **Hypothetical** | Construct a narrative-driven scenario not yet observed | Can explore tail risks, forward-looking | Subjective, may lack internal consistency |

**Designing Effective Scenarios — A 5-Step Framework**

```mermaid
flowchart TD
    A["Step 1: Identify key risk factors"] --> B["Step 2: Define the macro narrative"]
    B --> C["Step 3: Calibrate factor shocks"]
    C --> D["Step 4: Apply to portfolio"]
    D --> E["Step 5: Review, challenge, and update"]
```

**Worked Example — Hypothetical Scenario**

Aldridge Wealth Management wants to stress test its $2.4 billion multi-asset portfolio against a "Stagflation Resurgence" scenario.

**Step 1 — Key risk factors:** US equity prices, 10-year Treasury yield, USD/EUR rate, oil prices, credit spreads, inflation breakevens

**Step 2 — Narrative:** Supply-chain disruptions from a major geopolitical conflict drive oil to $140/bbl. Inflation surges to 7%, forcing aggressive Fed tightening. Growth stalls as consumer spending collapses.

**Step 3 — Factor shocks:**

| Factor | Current | Stressed | Change |
|---|---|---|---|
| S&P 500 | 5,280 | 4,224 | -20% |
| 10Y Treasury yield | 4.20% | 5.80% | +160 bps |
| Oil (WTI) | $78 | $140 | +79% |
| IG credit spreads | 95 bps | 210 bps | +115 bps |
| USD/EUR | 1.08 | 1.02 | USD strengthens 5.6% |

**Step 4 — Portfolio impact:**

| Sleeve | Exposure | Estimated Loss |
|---|---|---|
| US equities | $960M | -$192M |
| US IG bonds (DV01 x spread widening + rate shock) | $720M | -$108M |
| International equities (+ FX) | $480M | -$115M |
| Commodities allocation | $240M | +$48M |
| **Total portfolio loss** | | **-$367M (-15.3%)** |

**Step 5 — Challenge:** Is a simultaneous 20% equity decline and 160bp rate rise internally consistent? (Yes — this mirrors 2022 dynamics.) Would oil at $140 push rates even higher? (Possible — add a sensitivity band.)

**Best Practices:**
- Run at least 3-5 scenarios spanning different risk dimensions
- Include at least one "implausible but not impossible" scenario
- Update scenarios quarterly or when the risk environment shifts
- Present results alongside VaR for a multi-dimensional risk picture

For scenario analysis templates, visit our FRM Part I materials.

How do historical and hypothetical scenario analyses differ, and how should a risk manager design effective stress tests?

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