Andreas Flache

Andreas Flache

I use both computational modelling and empirical research to study cooperation and social integration in human societies, and how this relates to social networks. See http://www.gmw.rug.nl/~flache.

Location I am professor of Sociology at the University of Groningen, The Netherlands.

Activity

  • I guess it is fair to say that this is a littlebit more than just an assumption. There are literally hundreds of scientific studies on the effects of intergroup contact on prejudice. The upshot is that by and large it reduces prejudice, but we have a also learned a lot about the conditions under which it does or does not work. Some referenences: The classic is...

  • Indeed, as one good model is. Once we have a good simple model that makes us understand something, we have a useful basis to move on and make the model more complex in meaningful ways. An important question will then always be whether and under what condition a result of interest (e.g. opinion clustering) will hold up. Good suggestions have been made here in...

  • I can only agree with the comments above, the outcome of segregation in this example is not necessarily what people have been choosing for. They may prefer other outcomes , but the "institution" of free and uncoordinated individual decision making entails here segregation as unintended and - at least in this example - by most people undesired result. Thinking...

  • Your last question is very interesting to think about. When seeing an ABM people often say "I could have known this without the model". But such a model is just the start. Once we got it to do "the obvious" we have a tool to ask in an intellectually disciplined way what the consequences would be of different conditions and complications. For example, based on...

  • Quite right that the spatial structure of CAs is rather limited when compared to real social networks. CAs help to understand the basic properties of many dynamics and then a next step is to explore what happens if we assume more complex network structures. Which is what actually quite a few researchers do, for example Centola & Macy in their research on the...

  • Vanessa and Paula, I couldn't agree more. Self-organization may be part of the explanation of clustering but there are of course other possible exogenous factors like those you mention. In the end we also need empirical research to assess how much each possible factor contributes to explaining actual clustering patterns, and people conduct such studies for...

  • As hopefully will become clearer in what follows, CA models can be seen as a subclass of ABMs. CA models impose a particular spatial interaction structure and focus on influences from the local neighborhood on agents' behavior, which in turn is expressed in terms of changes of the state of cells or the spatial location of agents (moving). If you are...

  • Reference for research on intergroup contact: The classic is Allport (Allport, Gordon W. 1954. The Nature of Prejudice. Cambridge, UK: Addison-Wesley.), but there is very much follow-up research, see e.g. this overview paper here: Pettigrew & Tropp (2006), "A Meta-Analytic Test of Intergroup Contact Theory", Journal of Personality and Social Psychology, 2006,...

  • To be sure, no one here is saying that this is the "natural state of affairs". As you will have seen the article ends with "in the next article, we will look a bit more into what the model tells us about the conditions when segregation would arise. And we will relate Schelling’s model to real data about ethnic preferences". Have a look into Clark & Fossets...

  • For this model it seems to not matter whether you use NetLogo 4 or 5. You can run it with NetLogo 5.1.0. Just enter "Continue" when the warning message appears that this model was created under NetLogo 4. After that the models runs without problems as far as I could see. The author of the model is Ian Weaver, a contact address can be found on the site to which...

  • Good point! While indeed much interaction is not bounded locally in geographical space, important structural characteristics of 'real' social networks are similar to the structures we have in a CA. See also my reply to Diloram's comment below for more details and a reference to CA-based work exploring the effects of network structures on social influence...

  • Good point! There are some agent-based models that take into account that some features are more important than others and thus can shape the further process of opinion formation. For example, Baldassarri and Bearman proposed a model of polarization in the American Society in which they elaborated the idea that discussions in interaction focus on those issues...

  • Thanks for checking this! The link embedded in the text brings you to the same page "If you want to try it out yourself, you can use a NetLogo implementation of the >>Axelrod<< model." (http://ccl.northwestern.edu/netlogo/models/community/Dissemination%20of%20Culture)

  • Good point, this particular model always moves into a stable equilibrium. But to be sure, this is not inherent to the CA framework as such. Once you add for example some random noise (agents changing their opinions spontaneously with a small probability) or random movement (agents relocating with a small probability) or random interaction (agents sometimes...

  • Good point, Farid! I do of course agree that before we can use ABM for serious policy advice, these models need to be much more sophisticated, based on empirical input data and tested against empirical output data. In some areas, like traffic modelling or models of disease spreading, ABM modellers are quite successful in this. In other areas, like opinion...

  • Good points! Further on in this module we discuss Axelrod's model of "cultural dissemination" in which individuals have many different features. This model shows that social influence in combination with homophily (birds of a feather flock together) can produce clustering of like-minded people and alignment of their opinions across many dimensions (e.g....

  • Very good points. Further on in this module we discuss Axelrod's model of social influence. This models adds the assumption that you are more likely to interact with others who are more similar to yourself. This further promotes cluster formation and - indeed - the emergence of a small world in which people mostly interact with those who are similar to them...

  • Yes, there are CA models of what has been called "fads" or "cultural drift", based on Axelrod's model of opinion dynamics (see later in this module). For example, modelling work by physicists (Klemm, San Miguel) showed that if you add to Axelrod's original model a small chance of "random perturbation" of opinions, clusters can break down but also new "fads"...

  • Good point! CA can help to understand well what happens in a clustered world with local interaction. And while it is true that much interaction nowadays is not bounded by geographical space, we also know that the networks within which people interact are often strongly clustered. That is: typically people interact with others who are also connected to each...

  • Indeed, social psychologists point to this mechanisms, sometimes called "striving for uniqueness". Agent-based modellers have explored the consequences this may have for social influence dynamics. Broadly, if there is sufficient anti-conformism in combination with social influence, this can generate permanent diversity and clustering in society. See for...

  • This is obviously a deviation from reality. But not every deviation from reality is a problem in modelling and some are actually quite useful. In this case, we would first have to answer the question whether assuming a torus makes a big difference. Well, for many results of CA models it does not matter (you can try this out with many of the models in the...

  • Good to see you are already discussing the fundamental assumptions! A general definition of interaction would be any form of encounter in which an 'agent' (or, actor) responds to perceived actions of other agents in his local environment such that these other agents - in turn - respond to the actions of that focal agent. In that sense actions like moving into...

  • Axelrod's model has as a possible outcome that distinct and stable cultural groups arise that are so different from each other that no further influence between the groups will take place. This is very similar to the situation that you describe. But the reason that these groups emerge in this model is social influence. Social influence has in such a case led...

  • I fully agree that social-self organization does not imply that policy makers should not try to influence social dynamics in directions that can be seen as socially desirable (where it is of course a matter of democratic debate what that exactly means). But social self-organization also teaches us that social behavior is not easy to influence, can develop in...

  • Very interesting comment: "then as people travel more, interact more then gradually their views will coincide and everyone will co-exist peacefully (not much sign at the moment)! ". This is indeed an implication of Axelrod's model, but as so often it depends a lot on the assumptions you make. Elsewhere I have argued that actually the opposite is also possible,...

  • About the statement "none of the agents is dissatisfied in the final outcome": in modelling, it is very important to distinguish between purely analytical statements describing the behavior of a theoretical model, and statements about the real world. The statement above has a clear meaning within the context of the model. We have a definition of what an agent...

  • I know of at least one model by my my colleague Michael Maes and his co-author Lukas Bischofberger. See here: http://www.maes-sociology.eu/news/bestpaperaward
    One conclusion is that when people tend to link mainly to those they agree with, this may lead to opinion polarization.

  • Interesting idea to analyze the follow network from FutureLearn to see whether there is clustering! There are studies of the links between political blogs in the U.S., or of twitter networks showing clear evidence of clustering along partisan lines. See for example here for some instructive visualizations and background:...

  • I definitely agree that housing prices are also an important factor. But as it seems, so are ethnic preferences and various other factors (e.g perceptions of crime rates). The challenge for modellers is trying to understand how all these factors operate together. For example, whether differences in housing prices and income may amplify segregation dynamics, or...

  • There are models that include differences in wealth and housing prices. Some of this work can be found in the paper by Clark and Fosset to which I also refer in one of the articles about the Schelling model. Fosset also has a simulation model (simseg) that allows to play around with variation in things like income levels, housing prices, social status of...

  • If it is seriously flawed it should produce some central outcomes that can be empirically refuted. ABM is a tool that can help us to find such refutable predictions from a model.

  • I agree that for many social phenomena it is not so difficult to invent some model that can produce the phenomenon. That is why the assumptions we make in these models should be rooted in theoretical and empirical knowledge about human behavior. The assumptions of social influence and homophily do not just come from somewhere but have been tested in much...

  • Very interesting that you raise the point about Axelrod assuming a nominal opinion space. I can only agree that this is often an unrealistic assumption. Actually in some other paper with Michael W. Macy we showed how diversity can become much less likely once you assume continuous features on which agents can move towards each others' opinion in gradual steps ...

  • It certainly makes sense to assume that some features are less easily influenced than others. This could surely be built into this kind of model, but it is not yet in the program in NetLogo. An interesting implication may be that if there is consensus on such a hard-to-change feature, this may prevent clustering because agents always have something in common.

  • This is possible in the model. You may first pick A as focal agent who then interacts with B and adopts a trait of B on some feature. Then at some time later you may pick B and B interacts with A, then adopting a trait from A on some other feature. They more similar they become (as consequence of such interactions), the more likely they are to interact again.

  • Clearly in online networks people are not restricted to interacting with others within a close "distance" from them. But interestingly "clustering" can (and does) also occur quite a bit. In online networks you can choose people (or, say, blogs) based on their similarity to your opinions. This is also called homophily. If everyone does that, people end up in...

  • That could be a good justification for this assumption. It actually draws on an early version of Schelling's model, where the idea is that people have a perception about how a neighborhood (in the sense of a couple of hundred or maybe even thousands of households) is composed ethnically and then make their decision whether to stay or move to another...

  • I (obviously) agree with the argument in our paper that Axelrod's model produces (some) unrealistic results. But I think one should not conclude that therefore all models based on this approach must be unrealistic. To take up the example quoted above that Axelrod's model predicts diversity only for small populations: we show in our paper that a relatively...

  • Your understanding of the model is exactly right. I am also not sure how realistic it is... But then there are many examples of models that aim to introduce more realism in this type of modelling. One example is our more recent paper referred to in the text (Flache & Macy, 2011), but there are many others (you can e.g. find references in our paper to models...

  • Very important discussion. To be sure, models like this one do in no way imply a value statement about whether diversity is good or bad. But they may help to understand the conditions under which diversity emerges or is stable. Much research (e.g. in organizations, school classes, neighborhoods) shows that homophily is a fact of life, a very robust social...

  • Very interesting point. There are actually models of self-organization of hierarchies in animals that take into account differences in strength and 'personality', but also show how hierarchies can become self-reinforcing at some point. Interesting work in this area is done for example by Charlotte Hemelrijk and her group...