Complexity and Social Networks Blog: Bavelas revisited: hub-spoke vs all-channel networks

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23 April 2007

Bavelas revisited: hub-spoke vs all-channel networks

I ran a version of the “Bavelas experiments” in my “Building organizational social capital” class last week. The Bavelas experiments were conducted by Alex Bavelas and Harold Leavitt and collaborators in the Small Group Network Laboratory at MIT in the 1950s. The basic experiment is where members of a small group (size N) of subjects are each given a different symbol drawn from a set size N + 1. The task is for the entire group to figure out what symbol is missing. How the group can communicate is dictated by the experimenter, where certain channels are acceptable, and others not. In each round, each subject is allowed to pass a message to one other person. One of the provocative findings from this vein of research was that centralized networks—e.g., where there is a hub that communicates with everyone else but no one else can communicate with each other—tends to perform faster on this task than decentralized networks (in the extreme, where everyone can communicate with everyone else). The basic logic is that in decentralized networks information floats around inefficiently.

Follow up on this vein of research suggests that as the task gets more complex, that decentralized networks actually do better than centralized. An interesting and relevant critique of this research, by Guetzkow and Simon (1955), was that all-channel networks can and do sometimes perform better than hub-spoke networks. That is, the performance of all channel networks was contingent on how they were used. The original Bavelas findings were based on the fact that they were usually used badly.

When I conducted this experiment last year, it pretty much went as expected, except for in one case, where the hub misunderstood the experiment, which resulted (unsurprisingly) in very poor performance by that hub-spoke group. (This highlights that hub-spoke networks are highly dependent on the hub; again unsurprising.)

This year, it went quite differently, where the all-channel network did far better than the hub-spoke network. Both 6 person networks (we did this with two of each and had identical results) performed at their theoretical optimum, which, for the all-channel network was 4 rounds, and the hub-spoke network, 6 rounds. Why the contrast between the years? Because the hub-spoke groups kibitzed about how to communicate before we began the experiment. This only happened because (1) I did not initially explain that no communication (even if it was not about the symbols) was allowed; and (2) the room is so jammed that I could not tell exactly what was going on with the hub-spoke groups, who were in the back (and thus I could not stop them from kibitzing). The all-channel network groups decided, through their kibitzing, that they should all send their information to one person, who would then send the answer back to the group, which would then diffuse efficiently through the all-channel network. That is, per Guetzkow and Simon, they figured out the best way to use their communication capacity.

The interesting lesson to draw here is that all-channel networks (putting the overhead of having more ties aside for a moment) provide a reconfigurable capacity for task-relevant communication. If people are provided (or produce) “programs” about what the task type is, the resulting communication patterns will potentially be more efficient than if the network is hard wired.

It also raises an interesting question, a la Schelling, whether if one allowed some information about the participants in the experiments, and some information about the structure of the network, whether the all-channel network would perform better than it did in the Bavelas experiments. In the Bavelas experiments (as I recall), subjects did not know anything about each other and did not know the configuration of the network. Now imagine, for a moment, that you know what the configuration of the network is, and something about the other subjects; might focal point nodes emerge, to whom most information would be sent, resulting in increased information?

Bavelas, A. Communication patterns in task-oriented groups. J. Acoustical Soc. America 22 (1950), 725-730.

Guetzkow, H., and Simon, H.A. The impact of certain communication nets upon organization and performance in task-oriented groups. Mgmt. Sci. 1 (1955), 233-250.

Leavitt, H.J. Some effects of certain communication patterns on group performance. J. Abnormal and Social Psychol. 46 (1951), 38-50.

Also, see nice summary of research by Steve Borgatti.

Posted by David Lazer at April 23, 2007 9:17 AM

Comments

Well, yes, I think so - if the participants know who are the others and know a little bit about their backgrounds that will lead to different perceptions of the network hierarchy and therefore to tend to redirect information or ask for help to the members they perceive as more knowledgeable.
In the real world those perceptions and mechanics are built through time (trust and reliance) and space (availability).
Has anybody out there done something like you suggest David?

Posted by: Irene Lopez de Vallejo at April 23, 2007 9:46 AM

Just a quick, off-the-top-of-the-head (and certainly not informed with the literature background ...), re yours:

"The all-channel network groups decided, through their kibitzing, that they should all send their information to one person"

Does this mean that the 'all-channel' in effect transformed themselves into a 'hub and spoke'? perhaps with the advantage of a self-configuration that will 'work best'? but with the capacity for a quality 'self-configuration' depending on the capabilities and prior familiarity of the group?

Posted by: David Allen at April 23, 2007 11:35 AM

In response to Irene, not that I know of. However, if someone reads this post and think of exceptions, please do correct me. It would be neat for someone to pick up the baton on this vein of research.

And, David, you are more or less correct. Yes, the all-channel network configured itself to be centralized, inasmuch as everyone sent their initial signal to one person. However, in diffusing the information from that spoke, the information spread in a more decentralized fashion. On the bigger point, you are exactly right; the all channel network can reconfigure based on task. Of course, as I note, there can be a prohibitive overhead associated with maintaining that many ties, especially as groups get larger (the number of ties in an all-channel network goes up with the square of the size of the group).

Posted by: David Lazer at April 23, 2007 9:42 PM

Re:
"there can be a prohibitive overhead associated with maintaining that many ties [in an all-channel network]"

This could be the basis for an explanation why adaptive evolution finds human beings predisposed to hierarchy ...

Posted by: David Allen at April 23, 2007 11:26 PM

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