Good Judgment Open: The Superforecaster Platform Explained

Before Polymarket existed, before Kalshi had a CFTC license, a government-funded research project discovered something remarkable: a small group of ordinary people — no PhDs required — could out-predict CIA analysts, geopolitical experts, and professional forecasters on world events. They were called superforecasters.

Good Judgment Open (GJOpen) is the public platform that emerged from that research. It's free to join, hosts thousands of questions, and serves as both a forecasting training ground and a signal source for sharp Polymarket traders who know how to read it.

The Origin: The Good Judgment Project

Good Judgment Open traces back to the Good Judgment Project — a multi-year IARPA-funded tournament starting in 2011 to determine whether human forecasters could beat chance (and intelligence community baselines) on geopolitical questions.

The results, documented in Philip Tetlock's landmark book Superforecasting, showed that a subset of participants — roughly the top 2% — were dramatically better than everyone else:

• 60% more accurate than average forecasters
• Outperformed professional intelligence analysts with access to classified data
• Maintained their edge across years and question types
• Used specific, learnable thinking techniques — not innate genius

The company Good Judgment Inc. spun out of the project and launched Good Judgment Open as the public-facing platform where anyone can forecast alongside superforecasters.

How Good Judgment Open Works

GJOpen runs similarly to Metaculus but with a specific focus on geopolitical, economic, and policy questions — the domains where superforecasters have demonstrated the most dramatic edges.

Question Types

GJOpen questions typically ask for probabilities on verifiable binary or multiple-choice outcomes:

• Will Country X hold elections before Date Y?
• Will GDP growth exceed Z% in Q3?
• Will any member of Group A do B before C?
• Will Organization X announce Y before the end of the quarter?

Scoring System

Forecasters are scored using the Brier score — a proper scoring rule that penalizes both overconfidence and underconfidence. A perfect Brier score is 0.00. Chance is 0.25. Elite superforecasters consistently score below 0.10.

Your cumulative Brier score creates a leaderboard position that unlocks access to Superforecaster team questions — premium questions with higher-stakes geopolitical content that aren't visible to the general public.

The Superforecaster Mindset

Tetlock's research identified specific thinking patterns that distinguish superforecasters from average forecasters — all of which transfer directly to prediction market trading:

Using GJOpen for Polymarket Edge

The practical workflow for Polymarket traders:

1. Find the question on GJOpen— search for the same event that's priced on Polymarket. Many high-volume Polymarket markets have parallel GJOpen questions.
2. Read the top forecasters' rationales — GJOpen shows the reasoning behind forecasts. This is often more valuable than the number itself. Expert rationales surface evidence you may have missed.
3. Compare to Polymarket price — gaps of 5–10%+ warrant investigation. Gaps of 15%+ on well-researched questions are often genuine mispricings.
4. Validate with PolyMath tools — confirm positive EV with the EV Calculator, then size with Kelly Criterion.

GJOpen vs Metaculus — Which Is Better?

Use both. GJOpen has deeper expert commentary on geopolitical questions. Metaculus has broader coverage and a larger forecaster community. Together they cover virtually every major question that also appears on Polymarket or Kalshi.