Good Judgment Open vs Manifold Markets

Good Judgment Open (GJ Open) was launched in 2015 as the public-facing forecasting portal of Good Judgment Inc, a commercial spin-off originating from the landmark Good Judgment Project (GJP). Co-founded by Wharton professors Philip Tetlock and Barbara Mellers alongside UC Berkeley professor Don Moore, the platform stems from research funded by the US Intelligence Advanced Research Projects Activity (IARPA) Aggregative Contingent Estimation (ACE) tournament, which demonstrated that well-calibrated crowd ensembles systematically outperformed professional intelligence analysts.

Unlike financial orderbook prediction exchanges that rely on real-money or cryptocurrency pricing, GJ Open operates as a non-monetary, probability-based forecasting engine. Participants submit percentage probabilities on complex geopolitical, macroeconomic, public health, and environmental questions. Individual predictions are tracked over time and evaluated using Brier accuracy scores—a mathematical metric measuring probabilistic calibration and resolution accuracy.

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Manifold Markets was founded in December 2021 by former software engineers Austin Chen, James Grugett, and Stephen Grugett in San Francisco to democratize market creation and rapid crowd forecasting. Operating as a social prediction platform, Manifold allows any user to instantly deploy custom play-money prediction markets on arbitrary binary, multiple-choice, or numeric questions spanning technology, culture, geopolitics, and personal life.

The platform utilizes a proprietary play-money currency called "Mana" (Ṁ) combined with Automated Market Maker (AMM) liquidity pools to support real-time continuous trading. By granting question creators primary resolution authority and offering open, high-throughput developer APIs, Manifold built one of the world's most vibrant crowdsourced forecasting communities and hosts the annual Manifest forecasting conference.

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