When we published PG-0005, the market was at 51%. Today it is at 73% — moving from well below our forecast to well above it.
On September 18, ProbGap published its forecast for U.S. Q3 GDP growth of at least 3.0%.
At publication:
Market: 51%
ProbGap: 64%
Gap: +13 percentage points
The market disagreed with us.
Nine days later, that disagreement has disappeared.
Polymarket now prices ≥3.0% growth at approximately 73%.
That makes the comparison today:
Market: 73%
ProbGap: 64%
Gap: −9 percentage points
The market has moved 22 points since publication — and has now moved past our original forecast.
What changed?
The strongest supporting datapoint continues to come from the Atlanta Fed.
Its latest GDPNow estimate, published September 25, puts annualized real Q3 GDP growth at 5.0%.
That is slightly below the previous 5.1% estimate, but still comfortably above the 3.0% threshold in PG-0005.
Importantly, GDPNow has remained strong throughout September:
September 10: 4.4%
September 16: 5.1%
September 17: 5.1%
September 25: 5.0%
The next GDPNow update is scheduled for September 30.
This is what a track record should show
PG-0005 is useful precisely because the market did not stand still.
At publication, ProbGap was materially more bullish on the probability of ≥3% growth.
Since then, the market has repriced sharply in the same direction — and continued beyond our forecast.
That does not automatically mean our 64% estimate should be raised to 73%.
An independent forecast should not simply follow the prediction market whenever the price changes.
Instead, the right question is whether the underlying evidence has changed enough to justify a forecast revision.
GDPNow at 5.0% certainly strengthens the YES case.
But there is still meaningful uncertainty between a real-time nowcast and the official GDP release that ultimately resolves the market.
ProbGap forecast unchanged — for now
For the moment:
Market: 73%
ProbGap: 64%
Gap: −9 pp
We are keeping the published forecast at 64% pending a formal forecast review.
The important development today is the movement itself:
Publication: +13 pp ProbGap gap
Today: −9 pp ProbGap gap
A 22-point market move has completely reversed the original discrepancy.
PG-0005 remains open.
ProbGap identifies where independent forecasts differ from prediction-market prices — and tracks those forecasts through resolution.
Sources: Polymarket; Federal Reserve Bank of Atlanta. Market probabilities change continuously.