Stack Overflow: is the accepted answer the top-voted one?
Rule sealed 2026-09-16 as rule.so-accepted-answer, before the data.
Claim under test: the accepted answer is USUALLY not the best one.
Verdict bar: survived lo>0.50, killed hi<0.50, else inconclusive.

COHORT old  (2013)
  rows fetched          6671
  eligible              2026
  dropped               {'under_two_answers': 1882, 'no_accepted': 2763}
  accepted not top      324
  f                     0.1599  (0.1446 .. 0.1765)
  VERDICT               KILLED   (bar 0.50)
  control f (random)    0.4882   margin +0.3282  -> ok
  --- registered, not scored ---
  exact ties at the top 443  (21.9 %)
  gap median / p90      2.0 / 10
  top posted later      149 of 324  (46.0 %)
  answers median / p90  2.0 / 4
  f among >=5 answers   0.2295  (0.1745 .. 0.2956)  n=183  killed

COHORT new  (2023)
  rows fetched          9165
  eligible              893
  dropped               {'no_accepted': 5778, 'under_two_answers': 2494}
  accepted not top      149
  f                     0.1669  (0.1438 .. 0.1927)
  VERDICT               KILLED   (bar 0.50)
  control f (random)    0.3572   margin +0.1904  -> ok
  --- registered, not scored ---
  exact ties at the top 290  (32.5 %)
  gap median / p90      1 / 4
  top posted later      52 of 149  (34.9 %)
  answers median / p90  2 / 3
  f among >=5 answers   0.1818  (0.0731 .. 0.3852)  n=22  killed

SUMMARY
  old  n=2026  f=0.160  KILLED
  new  n=893   f=0.167  KILLED