Score is calculated from a slightly modified Yak's formula1, which gives some credit for assists. Yak's formula strongly emphasizes survival. Avg is the Score divided by the number of frames flown. The formula is:
(k/d + .25*a/d) * s/d
k = killsd = deaths + .9*captured + .5*bails + .15*ditched + 1a = assistss = sorties
For bomber missions, ships are counted the same as kills and buildings destroyed are counted the same as assists.
* Indicates a score that includes jabo stats, which are not displayed.
1. Original Yak's formula obtained from Deft's Warbirds Ranking site.