┌─────────────┬──────────────┐
VOLUME 222222 │    A.B.C    │    X.Y.Z     │
              └─────────────┴──────────────┘
 
Volume 222222 was mounted 3 times.
 
  Statistical mounts for A.B.C
                 = volume mounts (3)/data sets on volume (2)
                 = 1.5 statistical mounts per data set

Data sets A.B.C and X.Y.Z share Volume 222222. For these multifile data sets, the number of statistical mounts is an average of the number of mounts for the volume divided equally among all data sets on that volume (statistical mounts = number of mounts/number of data sets on a volume). So a volume mounted three times containing two data sets (3/2) equals 1.5 statistical mounts.