Category Archives: News

ECMS paper updated

A quick post to point out that the paper I just presented at ECMS 2013 in Ålesund, Norway has been updated to reflect the final revisions made before it entered the Proceedings volume (which is now published).  You can find the new citation and updated PDF on my Publications page.

I wasn’t sure what to expect from the conference, given the very broad selection of papers (141 papers in the Proceedings in total, which made the book itself enormous!).  But in the end it was a very productive week, characterised by interesting chats with colleagues in the midst of the most spectacularly lovely weather I think I’ve ever seen in Norway.

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Presenting at Eurostat / UNECE Work Session on Population Projections

We got some pleasing news on Friday: our abstract entitled From agent-based models to statistical emulators has been accepted for presentation at the Eurostat/UNECE Work Session on Population Projections in Rome, Italy from 29 – 31 October 2013.   This will be a great opportunity for me to link up with more demographers and gain greater exposure to that community.  As ever I’m curious to find out how our unconventional methods of modelling will be received!

Our abstract is below:

From agent-based models to statistical emulators

Jakub Bijak, Jason Hilton and Eric Silverman

University of Southampton, Southampton, SO17 1BJ, United Kingdom

Contact author: j.bijak@soton.ac.uk

Proposed for the strand on «New methodologies» Eurostat / UNECE Work Session on Population Projections; Rome, 29–31 October 2013

Contemporary demographic micro-simulations are largely concerned with populations of statistical individuals, whose life courses can be inferred from empirical information (Courgeau 2012). In contrast, agent-based models study simulated individuals, for whom certain behavioural rules are assumed. We wish to bring these two approaches closer together by coupling the rule-based explanations driving the agent-based model with observed data. We also propose a method to analyse the statistical properties of such models, based on the notion of statistical emulators (Kennedy & O’Hagan 2001; Oakley & O’Hagan 2002).

In this paper, we present a Semi-Artificial Model of Population, which aims to bridge demographic micro-simulation and agent-based traditions. We extend the ‘Wedding Ring’ agent-based model of marriage formation (Billari et al. 2007) to include empirical information on the natural population change for the United Kingdom alongside with the behavioural explanations that drive the observed demographic trends. The mortality and fertility rates in this population are drawn from UK population data for 1951–2011 and forecasts until 2250 obtained from Lee-Carter models. We then utilise a Gaussian process emulator – a statistical model of the base model – to analyse the impact of selected parameters on two key simulation outputs: population size and share of agents with partners. A sensitivity analysis is attempted, aiming to assess the relative importance of different inputs.

The resulting multi-state model of population dynamics is argued to have enhanced predictive capacity as compared to the original specification of the Wedding Ring, but there are some trade-offs between the outputs considered. The sensitivity analysis indicates a key role of social pressure in the modelled partnership formation process. We posit that the presented method allows for generating coherent, multi-level agent-based scenarios aligned with selected aspects of empirical demographic reality. Emulators permit a statistical analysis of the model properties and help select plausible parameter values. Given non-linearities in agent-based models such as the Wedding Ring, and the presence of feedback loops, the uncertainty of the model may be impossible to assess directly with traditional statistical methods. The use of statistical emulators offers a way forward.

Billari, F., Aparicio Diaz, B., Fent, T. and Prskawetz, A. (2007) The “Wedding–Ring”. An agent–based marriage model based on social interaction. Demographic Research, 17(3): 59–82.

Courgeau, D. (2012). Probability and Social Science. Methodological Relationships between the two Approaches. Dordrecht: Springer.

Kennedy, M., and O’Hagan, T. (2001) Bayesian Calibration of Computer Models. Journal of the Royal Statistical Society, Series B, 63(3), pp. 425–464.

Oakley, J. and O’Hagan, A. (2002) Bayesian inference for the uncertainty distribution of computer model outputs. Biometrika, 89(4), pp. 769–784.

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Presenting at JSM 2013, Montreal

This August I’ll be presenting a paper at JSM 2013 in Montreal.  This piece of work is a joint effort by Jakub Bijak, Jason Hilton and myself, titled Statistical versus Agent-Based Demography: Bridging the Gap with Gaussian Process Emulators (click the link to see the abstract).

This conference will be, shall we say, rather enormous.  There are apparently more than 6,000 statisticians due to attend (!), and given that I’m not a statistician myself, I suspect I’m in for some challenging questions.

I’m also ashamed to admit that this will be my first-ever visit to Canada, despite the fact that I spent a significant chunk of my life growing up in Pennsylvania, just slightly to the south.  I’m looking forward to visiting our northern friends — my only regret is that my visit falls well outside of hockey season, which is by far the best sport, and I’ve little doubt Canadians are by far the best people to watch it with.  Ah, well — gives me an excuse to go back another time!  I’ll have to make do with my NHL Gamecenter Live subscription until then.

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Paper accepted to ECMS 2013

I’ve just had a paper accepted to the European Conference on Modelling and Simulation 2013 which is being held from 27-30 May in Ålesund, Norway.  The paper is titled Simulating the Cost of Social Care in an Ageing Population and was written by myself, Jason Hilton, Jason Noble, and Jakub Bijak.  We were accepted to the Policy Modelling track, so I’m hoping for some interesting feedback from other researchers who may be working on projects aimed at health and social care.

The reviews were very positive on the whole, so we’re pleased about that!  Corrections are still to come before the paper enters the Proceedings, but in the meantime you can find the submitted draft here.

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Book review published

The review of Daniel Courgeau’s 2012 volume Probability and Social Science my colleague Jakub Bijak and I put together has now been published!

You can find it here.  Sadly the article is behind a paywall, at least for the moment, but if you require a pre-print version please get in touch.

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Journal paper accepted!

I’m pleased to say that I’ve had a paper accepted to a journal this week: an article written by myself and my colleagues Jakub Bijak, Jason Hilton, Jason Noble and Viet Cao.  The paper is called “When Demography Met Social Simulation: A Tale of Two Modelling Approaches” and will appear in the Journal of Artificial Societies and Social Simulation (JASSS) as soon as we submit the final version with a few small changes.

JASSS is an open-access journal, so once the article is available I’ll post a link here.  Hopefully this run of good fortune will continue as I submit my paper to ECMS 2013 in Norway on 15 February!

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Book review in press

My colleague Jakub Bijak and I recently put together a book review on Daniel Courgeau’s 2012 book for Springer ‘Probability and Social Science‘.  Jakub is a demographer and I’m an agent-based modeller with interests in social systems, so we decided to put our heads together and do an interdisciplinary book review for Daniel’s volume.  Spoiler alert: it’s a very good book.

Our review is in the journal Population Studies and will be available online soon — we just received information on how to make it open-access today 🙂

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Science and the press: Who’s to blame?

There’s an interesting article in the New Yorker today about Neuroscience called ‘Neuroscience Fiction’, which comments about the recent fashion for neuro-everything: neuroeconomics, neuroethics, etc. etc.  Perhaps, finally, we’re beginning to reach the end of this trend?  The article implies that we are, which is good news — yet this doesn’t erase the fact that the past two decades of this indicate science is becoming increasingly dominated by what sells rather than by what is useful.

That article links to another by Alissa Quart which has an interesting quote on this:

“A team of British scientists recently analyzed nearly 3,000 neuroscientific articles published in the British press between 2000 and 2010 and found that the media regularly distorts and embellishes the findings of scientific studies. Writing in the journal Neuron, the researchers concluded that “logically irrelevant neuroscience information imbues an argument with authoritative, scientific credibility.” Another way of saying this is that bogus science gives vague, undisciplined thinking the look of seriousness and truth.

The problem isn’t solely that self-appointed scientists often jump to faulty conclusions about neuroscience. It’s also that they are part of a larger cultural tendency, in which neuroscientific explanations eclipse historical, political, economic, literary and journalistic interpretations of experience. A number of the neuro doubters are also humanities scholars who question the way that neuroscience has seeped into their disciplines, creating phenomena like neuro law, which, in part, uses the evidence of damaged brains as the basis for legal defense of people accused of heinous crimes, or neuroaesthetics, a trendy blend of art history and neuroscience.”

In science we’re very quick to blame the science journalists for willfully distorting research to make headlines.  Yet as Alissa points out, the researchers themselves are the ones pushing a fair bit of this nonsense — and they don’t necessarily speak up when their findings hit the headlines, distorted or not.  We’re in an environment where competition for funding is paramount, where permanent jobs are scarcer than ever, and where the pressure to find a unique niche is extremely high as a result — so creating that niche sometimes becomes more critical than performing good research.  We sometimes end up trying to squeeze together whatever ideas we can find into a lump just big enough to produce another published paper, then see how far we can milk it.

Speaking personally I know that I roll my eyes whenever I see one of the endless procession of papers in my field that applies autopoiesis to everything in the world ever.  I believe it’s part of the same process, on the whole, and it’s something we need to find a way to curtail.

With that in mind, where do our responsibilities lie here?  Do we call out our colleagues when they do dumb stuff, or do we direct our ire at nonsense only when it hits the popular press?  Do we try to keep our own community in line, and in doing so risk alienation (a true disaster for those of us low on the career ladder desperate for networking opportunities)?

It’s a difficult question.  After all, many of our colleagues do dumb stuff because they believe that dumb stuff, and so taking them to task over it is very unlikely to be productive.  I know I’ve certainly decided that someone is a jerk when they criticised me for reasons I believed to be ill-founded.  In the end, my paper stayed how it was, and the only thing that changed was that I resolved never to endorse or otherwise encourage the work of that individual.

Of course, my paper may very well have been dumb and I just simply don’t see it, but even if that is the case at this point the vast majority of scientific papers are dumb and/or uninteresting — so where do we draw the line?  How do we pick the particularly egregiously dumb stuff out of the endless piles that science produces these days?  Isn’t a certain amount of dumbness a necessary precursor to doing something of greater interest, a byproduct of early explorations?

My feeling is that science is now reaching a critical decision point in this respect.  Last year the UK alone published 124,000 journal articles.  Out of those, I expect we could skip at least 99% of these without losing much — very few papers have truly ground-breaking results to report.  At some stage we have to find a way to reduce this pressure to publish anything and everything at all costs, or we will simply drown in the resulting mess — and all the while, unscrupulous types will craft some of that mess into misleading headlines to make a buck or to build a reputation.

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Submitted a paper to IUSSP

Just yesterday my colleagues Jakub Bijak and Jason Hilton and myself submitted a paper (4-page extended abstract, with a paper to follow if accepted) to the XXVII IUSSP Population Conference, to be held in Busan, South Korea next August.  The paper is titled “Statistical Individuals and Simulated Individuals: Analysing Agent-Based Demographic Models with Gaussian Process Emulators“, which is a very long title… need to take a rest after saying all that.  The content is essentially a distillation of our recent work on agent-based models for the study of population dynamics, with an emphasis on the potential impact of this type of simulation methodology on event-history analysis.

The conference is run by the IUSSP, the International Union for the Scientific Study of Population, based in Paris.  The attendees will be 2-3,000 demographers across all areas of the discipline, so this will hopefully be my first opportunity to be on hand to present our recent work to the demography community.  I’m very interested to see how these conferences work; my field is quite small in comparison, and our big conferences are perhaps 1/10th the size of this one!

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Back in Southampton

I’ve returned to the UK now after a lengthy sojourn in East Asia, which turned out to be genuinely life-changing.  Following an exciting and interesting conference in Taipei, I traveled to Tokyo, where I got married (!), and enjoyed 3 fantastic weeks of relaxation and exploration with my partner.

Future posts will get back into more academic matters as I settle into my normal patterns once again.  I suspect there may be some exciting research developments on hand in the near future….

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