## What Is Stress Testing?

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### Purpose and scope
- Stress tests assess whether financial institutions and the financial system can withstand adverse events by examining solvency (enough capital to absorb losses) and liquidity (enough cash or liquid assets to meet withdrawals and debts).
- Typical questions addressed:
  - Can banks survive a recession if half of their mortgage clients stop paying debts?
  - Do insurers have enough to pay claims after a magnitude 8 earthquake?
- Historical context:
  - Attention to stress testing increased during the 2008 global financial crisis when major institutions failed or required multi‑billion‑dollar bailouts.
  - The IMF adopted stress testing in response to the Asian financial crisis of 1997 and incorporated them into the Financial Sector Assessment Program run jointly by the IMF and the World Bank since 1999.

### Key mechanics and illustrative figures
- Solvency example:
  - If a bank loses $1 billion when house prices drop by 50 percent, the bank can survive if its capital is $10 billion but not if it is $1 billion.
- Liquidity example:
  - If depositors suddenly withdraw $50 million and the bank cannot borrow to replace those deposits, it can survive if it owns quickly marketable assets (for example, government bonds).
- Stress tests use adverse scenarios that are severe yet plausible (low‑probability events with potentially catastrophic consequences).
  - Examples of severe scenarios: a once‑in‑a‑century earthquake, a repeat of the 2008 financial crisis, or a government debt default.
  - Implausible hypotheticals (for example, a Martian invasion) are excluded.

### Scenario design and transmission channels
- Design process:
  - Start with a country‑specific list of potential risks (for example, a major decline in manufacturing in a factory‑dependent economy; a terrorist attack in a tourism‑dependent country).
  - Develop a storyline and estimate how variables such as GDP and interest rates react under the scenario.
- Transmission to bank health:
  - Gauge how households and companies would behave (how many continue paying debts; how deposit withdrawals evolve).
  - Measure impacts on banks’ liquidity and capital based on client behavior and asset price movements.
- Systemic effects:
  - Connections among banks mean failures can ripple through the financial system (for example, if banks stop lending, firms may shrink and lay off workers; families may be unable to buy homes without mortgage credit).

### Emerging risks and expanding coverage
- Stress tests increasingly cover nonbank financial service providers and novel risk sources:
  - Mutual funds, insurance companies, and other nonbank providers.
  - New financial technologies affecting profitability of existing firms.
  - Operational dependencies such as banks’ reliance on third parties for cloud computing.
- Climate change risks:
  - Physical risks: increasing frequency and intensity of floods, droughts, and other natural disasters that can cause insurer losses or unaffordable premiums for households.
  - Transitional risks: policy shifts (for example, adoption of a carbon tax) that can cause industry declines (for example, coal), loan defaults, and value losses on bonds and equities.

### IMF focus and public stress tests
- IMF approach:
  - Focuses on the financial system as a whole rather than solely on individual institutions.
  - Once risks are identified, the assessment recommends ways national authorities can reduce risks before they materialize and control damage if they occur.
- Other authorities:
  - In the wake of 2008, authorities in the United States, the euro area, and elsewhere used stress tests and made results public to bolster confidence, focusing on identifying weaknesses in individual banks and measures to restore or close them.

### Data, limitations, and best use
- Data requirements:
  - Stress tests must use reliable, timely, and detailed data, including historical data covering turbulent episodes and periods of calm.
  - Incomplete or inaccurate data yield unreliable results and can provide a false sense of comfort.
- Complementary tools:
  - Stress tests are not stand‑alone; full risk analysis should combine stress tests with other quantitative and qualitative tools.
  - Financial stability assessments should be complemented by reviews of a country’s financial sector policies, oversight framework, and financial safety nets (for example, the existence and scope of deposit insurance).

*Martin Čihák, Hiroko Oura, and Liliana Schumacher; Finance & Development, September 2019.*

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_Source: https://www.imf.org/-/media/files/publications/fandd/article/2019/september/what-is-stress-testing-basics.pdf_