Market Efficiency Tester

Run formal weak-form efficiency tests on any ticker — autocorrelation, runs, Ljung-Box, and variance-ratio statistics, each with a plain-English interpretation. APT tab fits a Fama-French three-factor regression.

Interactive Lab

Efficiency Tester

Empirical weak-form tests — runs, autocorrelation, Ljung-Box, variance ratio + APT

Ticker

US/global Yahoo symbol

Period

Quick:

Pick a ticker and click "Run Tests". The lab fetches up to 10y of daily prices and runs four formal weak-form efficiency tests on the daily return series.

The Efficient Market Hypothesis says you can't predict tomorrow's price from today's information - returns should look random. We test this with three classic statistical tests: autocorrelation (do returns predict the next return?), runs test (are streaks of up/down days too long or too short?), and Lo-MacKinlay variance ratio (does volatility scale linearly with horizon?).

Every Lab is grounded in standard textbook math (Bodie / Kane / Marcus, Fabozzi, Tandelilin). Read the full methodology in the How It Works panel above.