These are the character stats modifiers:
 
Attributes:     0-7        8-12      13-17         18+
Strength         -5        --          +5            +10
Dexerity         -5        --          +5            +10
Intellignece     -5        --          +5            +10


Strength:  Climb, Jump, Swim, H-T-H

Dexerity:  Handgun,  Rifle,  SMG,  Knife,  Bayonet,  Move silently,  Shotgun

Intellignece:  All Crew served weapons,  All special weapons,  Demolitions, Boobytrap,  Communication,  Observation,  Scuba,  Interrigation