The behaviour of a group can, to some extent, be predicted using knowledge of its individuals. However, this very much depends on what sort of group you are asking about. Here are some examples:
A Group (flock) of Sheep
Sheep are fairly predictable at the best of times so you're off to a good start here. The thing about sheep is that they tend to do what other sheep do. So when one goes one way, you can predict with some conviction that the others will follow.
A Group (bunch) of bananas
Bananas are the least individualistic of fruits. They have almost no independent thoughts at all. This is particularly true when they're in a bunch, which seems to leave them apathetic and compliant. And, very, very, easy to predict.
A Group of People
This category is altogether different. A group of people each brings her or his own ideas and methods to the party. Their behaviour as a unity is almost impossible to predict with any accuracy.