From dictatorship and heirarchical, and consensus to popular choice, and even to egalitarian anarchy, there are many different types of group structure. A group's structure can be very important in its effectiveness in acheiving its goals. Canc2 had a taste of them all, at least in some way or another. As we progressed from pre-ride organisation to day 1 of riding, and then developing our own group styles, noting our strengths and weaknesses, our structure changed. We even experimented with different structures and decision making processes in an attempt to acheive our goals more efficiently and successfully, and to make the experience more rewarding for us, both as a group and as individuals. Easy! you say? - probably not, but getting your group structure and decision making processes functioning well can be incredibly rewarding.
Dictatorship
Central control unit has complete responsibility for decisions. This structure often goes hand in hand with repressed or oppressed societies, and can also be very handy in rescue situations, where there may only be one or two cognizant people. There would have been a trivial form of dictatorship in the formation stages of Canc2 (i.e. when there was only 1 or 2 people involved), but we quickly moved to a more cooperative operation.
Heirarchy
A system of delegated power, with the lower units able to make decisions within certain limits, and the upper levels maintaining powers of veto. This can be used when a group grows beyond the efficient handling abilities of a single control unit. During organisation, and in the beginning stages of the ride, we had different people and groups responsible for different functions (e.g. food, media, itinerary, finance). This does help in knowing where to direct concerns and information, and can function very well if the ability of each part of the heirarchy is known to be consumate with their area of control. You can have a flat heirarchy, or highly-tiered heirarchy. We attempted to set up a completely flat heirarchy covering most ride aspects, and then make the central position of power redundant (and then removing it). There were some concerns over the effectiveness and ability of some of the groups, which prompted pushes to other group structures.
Consensus
A structure where decisions are made only when everyone agrees to them. Operates when people are willing to give and take to meet the needs of the group. A big advantage of consensus decision making is that all parties are aware of all decisions, and when people aprrove of decisions, they are likely to follow them. We took great pains to come to 'consensus' decisions, with very lengthy discussions, but had enormous trouble acting out those decisions. After we noticed the non-commitment to decisions, we realised that people were agreeing to decisions only verbally, but not mentally - there were situations where people were not prepared to change their stand, and it became too emotionally draining to try to get everybody else to agree with one person's staunch point of view, so it seemed we were forcing people into consensus. It is here that we tried to tweak the consensus structure, by demanding less than complete consensus (e.g. 80 percent agreement, or agreement of all present when not everybody was there).
Popular Choice
Decisions are made when most people agree to them. Can be difficult to enforce when many people are not in agreement, and does not provide a strong forum for listening to people's concerns, but is very easy to make decisions. We didn't operate on popular choice very much, as people were keen to at least have their viewpoint heard and understood.
Egalitarian Anarchy
More of an unstable equilibrium than a structure of choice, but a structure nonetheless. A system of equal power, and freedom from any other constraints. Like politics, and business people, decisions are often made 'on the sly' and not in the public arena. At different times, people became unhappy with the group structure, with decisions, with plans or other popular constraints, and went about discussing their ideas with others, or simply actioning events that others may not have agreed to. This can be a realistic and progressive structure when strong, creative people need a variety of freedom and conformity to put thoughts into actions for a common goal. There were times when we decided we were losing effectiveness, and thus attempted a push toward one of the other structures.
...What structure is right for us?
It is a real achievement to get a group structure working successfully, with its participants committed to the structure and the outputs. I don't know the secret, but I imagine it's much about getting the right structure for a particular group of people. You may need to combine structures to get the right mix, particularly in larger groups. For example, you may have a heirarchical decision making structure, with one arm being based on consensus, another based on dictatorship, and yet another on popular choice.