I would say the answer is that the game is determined 100% by probability if all players play the game "correctly". Here is why. Let us first define "correctly". It doesn't really matter what you think is correct or this example as long as all the other players also think the same rules of strategy are "correct" and play the same way. For example this is the most basic common strategies employed by players 1. do not pass a biddable hand. 2. do count upon your partner for one trick. 3. do not trump your partner's ace. 4. do trump your partner's king. 5. do lead trump to your partner's order. 6. do not lead trump to your opponent's order. 7. if you order trump, lead your right bower 8. do not Order the right bower unto thy partner's hand unless you can go alone. 9. Go alone whenever you can, unless you havw eight or nine points. If everybody always follows these rules, if you play enough games to balance everythng out. In this case there is no thinking in the game. Who will win will depend totaly on the cards dealt and if enough tricks are played, probably on the order of a few hundred, the amount of points earned by both teams will even out. These rules are a good start but the skill of the game is to know when to break the rules. Say for instance trumping your partners ace becuase your know your oppenent will also.(just don't trump your partners ace with a nine or a ten) Then depending on how good the players are, the game shifts away from 100% probability to more skill than probability. It should also be mentioned that if one team knows these rules and a beginner team doesn't and they play, the team following the rules will win most of the time, but not because of skill.