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Codeforces 1400+ cohort study (2021 to 2026-10-08)
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Cohort: users rated >= 1400 at some point in 2021 AND still competing (>= 1 rated contest since 2025-01-01). 746 users.
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Source: Codeforces API (user.ratedList, user.rating), fetched 2026-10-08. Ratings are the rating after the user's last rated contest on or before each checkpoint date.
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Blank rating = user had no rating yet on that date. Blank country = not set on the profile.
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Sheets: 'All users' (ratings per checkpoint + 3 delta columns), 'Changes' (change between consecutive checkpoints), 'Summary' (cohort stats per checkpoint), 'Checkpoints' (dates).
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Delta columns and the Changes/Summary sheets are formulas, so they update if you edit a rating. Use the filter arrows to sort or filter by country, segment, etc.
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Delta Growth = ICPC (Sep 2025) minus Jan 2021. Delta Decline = Now minus ICPC. Delta Total = Now minus Jan 2021.
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Caveats: survivorship bias (only users still active are included); correlation with AI release dates is not causation; 2026 AI release dates are approximate (marked 'approx').
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