How we test

Every test compares a rule with simply buying and holding the same index over the same period.

Data

US results use daily S&P 500 total return data back to 1928 and Robert Shiller's monthly data back to 1871. International results use national index and country ETF data for up to 47 markets, including Korea.

Costs

Each trade pays 0.15% one way.

Checks before we call something real

We test the period before the idea was published, the period after it, and many markets at once. We count years, not markets, when markets move together. A result that disappears after removing a few extreme years is reported as fragile.