Final answer:
A decision made by a group is often called a consensus. This process can be influenced by groupthink, where decisions align with a perceived group consensus, and is guided by various voting rules and considerations such as a quorum and transaction costs.
Step-by-step explanation:
A decision made or an idea agreed upon by a group is often referred to as a consensus. In collective decision-making, there may be biases towards the status quo, majority rules, supermajority rules, or the need for compromise. Voting rules play a crucial role in how a decision is reached, often requiring a plurality or a unanimity for important issues. The term for when group members modify their opinions to match the group consensus is known as groupthink, a concept that can both facilitate group cohesion and potentially lead to unchallenged decision-making.
When groups face decisions that can influence all members, such as policies on climate change or resource management like the tragedy of the commons, the decision-making process involves weighing various transaction costs and the need to achieve a quorum for actionable decisions. For acephalous groups or in the absence of an official leader, the decision-making process tends to be informal and aims at reaching a consensus through group discussion.