Stock chart prediction without lookahead bias

Historical charts make prediction practice convenient, but they also make cheating effortless. A familiar crash, a famous ticker shape or an indicator calculated with future data can turn hindsight into apparent skill. That is lookahead bias.

A fair stock chart prediction exercise freezes the information set at one decision point. Read the Tape shows 60 sessions, calculates every signal from data available by the last visible close, and keeps the next five sessions on the server until a call is submitted.

The obvious leaks

Ticker, calendar dates and absolute price can identify an episode. Corporate names invite knowledge of earnings or news that came later. Removing labels and normalising price blocks most of these shortcuts while preserving return shape.

The subtle leaks

Indicators can leak too. A centred moving average, a scaler fit on the whole series or a chart range set using hidden highs and lows lets future observations influence what the player sees. Signals and display bounds must stop at the decision bar.

A reproducible daily sample

Each daily chart is selected from a deterministic date-and-slot seed and persisted once dealt. Everyone sees the same tape, and a restart cannot silently replace a difficult chart. The historical window ends well in the past, keeping the outcome fully settled.

What no-lookahead does not solve

A clean test does not prove technical analysis works. It only ensures the question was asked honestly. Selection bias, regime changes and the small sample from five charts a day still matter, which is why a long calibration record beats a memorable result.

Questions