Field-strength adjustment
also: adjusted strokes vs field · adj_vs_field
Strokes versus the field, corrected for how good the players in that field were.
Formula
score = course-day difficulty - player skill, solved over every round; adj_vs_field = expected average-player score - player's scoreEach round's field average is a mix of the course and the players. Solving for both at once, over every round of a tour, separates them: the expected score of an average tour player on that course that day, and each player's skill.
The adjusted number is what the rating is built from. A rating of 2.0 means two strokes a round better than an average player on the same tour.
The common mistake
Ratings are per tour: an LPGA 2.0 and a PGA Tour 2.0 are each measured against their own tour's players, not against each other.
Where to get it
Related
Field-strength adjustment from the API
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