Group attribution error is the assumption that decisions made by a group are representative of the feelings and beliefs of all members of that group.
For instance, in business many times a decision is made be a committee. It is easy for others affected by such a decision to assume that all members of the committee were in favor and supportive of the decision when only a majority of the committee was needed to approve a decision. Frequently in group decision making situations group dynamics (such as conformity) can influence decision making and cause individual preferences to be downplayed or ignored in order to maintain group cohesion.