Sometimes, you just know that the authors of an article you are reading, have had a lot of fun while writing it. The amount of fun just radiates from the pages (or your screen, in the digital age), and somehow, these articles are often the really interesting ones as well. Perhaps this has something to do with the authors feeling certain about their work and their grasp on it.

It must have been pleasant days in the `laboratories’ of Iannaccone and Makowsky when they wrote their article in `Agent-Based Explanations’ of religious dynamics. They start their article with a thought-experiment concerning a magic trick, have named the model they propose MARS (multi-agent religion simulation), and titled their paragraphs with variations as `Life on MARS’ and `Exploring MARS’. 

Despite all the fun, the authors have addressed an important problem in the study of regional segregation of religious (and non-religious) people. Regarding this religious regionalism in America they describe an apparent paradox of persistent mobility and persistent regionalism. The standard-approach to tackle such a problem (variants of regression analysis) fails, for it does not provide a “coherent model linking individual behavior to aggregate outcomes and vice versa”, thereby “ignoring social structure”. I gave an example of this problem of aggregation earlier (in Dutch), which illustrated how one can easily be led to the wrong conclusions, when the social restrictions people act within are not taken into account. 

In order to overcome such problems in the study of religion, Iannaccone and Makowsky have taken the famous Schelling-model and altered it to their needs. The basic version of the Schelling simulation model investigates locations people choose to live and the (segregational) consequences of these choices. The model is famous for showing how very small preferences for living amongst similar people will lead to large degrees of segregation.

Iannaccone and Makowsky have “turned the Schelling-model around”, meaning that people do not adjusttheir location to live based on their preferences, but adjust their preferences based on the location they live in and the neighbors they have. More specifically, the authors simulate whether or not people change their religious preferences (church membership, strength of conviction) based on the preferences of the people directly surrounding them. Moreover,  the MARS simulation model allows the researchers to `solve’ the paradox of persistent religious regionalism by showing that this pattern emerges from their simulations when individuals have both moderate levels of social conformity (being influenced by other people’s beliefs) and personal identity (adhering to own religious beliefs). 

In subsequent examples the authors show the flexibility of the MARS models (which can be seen and played interactively with on www.marsmodels.com). It is illustrated that the model is able to take into account Schelling-like preferences; that is the preferences people have when they select a new place to live, for instance amongst people of a similar religious conviction. It also is capable of simulating the impact of a ‘religious superstar’, that is a strong and influential person, and finally it allows immigration, that is an increase in the number of people present in a specific area. The model is also capable of not only investigating whether or not people are a member of church, but also takes into account which church one is member of, the strength of the religious conviction, changing religiousness without moving, and most of all: the preferences of individuals can be somewhat randomized so that not a single individual has exactly identical preferences (just like real life). 

All in all, I would say that the authors have succeeded in building a very interesting and flexible simulation model, the full power of which is only illustrated in the article. More than a solution to the single problem of the “paradox of persistent religious regionalism”, they have offered a perspective which will probably solve many problems in the (near) future.

There are however two characteristics to the (present) model that I do have some problems with. I’m sure they can be solved rather easily, but to my opinion that would bring enormous improvements to the model. The problems are basically: in real life people aren’t forced to move, and more in general: `where’s reality?’.  

To start with the first problem: since the authors turned the Schelling-model around, people in the simulation are randomly forced to move to another location. This is only valid under the assumption that moving has nothing to do with religious preferences. The authors cite additional research showing that indeed religious preferences hardly influence the choice to move. However, these are motivations of moving people, and thereby does not take into account the people that do not move at all. That might still be religiously motivated. Additionally, the assumption the authors make is only valid under the condition that nothing related to religious preferences (i.e. educational level, social economic status, gender, spouse) is related to the motivations of moving as well, for otherwise there is the alternative explanation for the outcome of segregation based on self-selection. I do not believe that this strong assumption can hold, and therefore the motivation for moving (or not moving) should be taken into account in the model. That would lead to a truly dynamic perspective.

The other issue, `where’s reality’, probably entails the need for a more elaborate extension of the model. Indeed, the model allows the authors to show that the combination of moderate values of both social conformity and personal identity allows for the explanation of the paradox of persistent religious regionalism. But is it a real explanation, or just a possible one. For starters, I would argue that it should be shown as well that these moderate values indeed prevail, for instance by using survey data. But, then again, we are almost back at the beginning, for the survey data does not allow for the aggregation that was achieved using the simulation model (MARS). A thought-provoking solution to this problem is suggested by Peter Hedström, who in his book `Dissecting the Social’ suggests that the actors of any simulation model should be `calibrated’ using observations, such as surveys. Basically, this would mean that the MARS simulation model should be able to replicate the persistent religious regionalism, when all actors are individually modeled after representative survey data. Technically, this would require the model to incorporate for each actor a vector of background-characteristics similar to many of the variables often used in other types of research on this subject, so that each actor represents a respondent from certain surveys. Additionally, from this it follows that the number of actors should preferably be close or identical to the number of (large scale) surveys. Only then we could consider the possible explanations offered by the MARS model (or any other simulation model, for that matter) as real explanations. 

All in all, I think that Iannaccone and Makowsky have developed a very interesting perspective and a powerful explanatory framework, drawing from mechanism-based explanations. There is some work to be done, but despite that the model already shows its potential. I’ll be looking forward to new publications based on this work, but for now, I’m off to play some more with the interactive MARS-models on www.marsmodels.com.

IANNACCONE, L.R., MAKOWSKY, M.D. (2007). Accidental Atheists? Agent-Based Explanations for the Persistence of Religious Regionalism. Journal for the Scientific Study of Religion, 46(1), 1-16. DOI: 10.1111/j.1468-5906.2007.00337.x

Schelling, T.C. (1971). Dynamic models of segregation. Journal of Mathematical Sociology, 1(2), 143-186.