About analysing crowd videos – a few years ago when I was running a project to develop guidelines on research ethics (including data protection regulations) a poor chap came up to me at a conference and said that he had hoped to do some research on crowd behaviour at football matches (to prevent another Hillsborough disaster) by analysing videos of crowd movements. However he was told by his university ethics committee that he could only do so if he got individual permission from every member of the crowd! But I suppose the police are under no such constraints..

Ursula Huws

 

 

From: email list for Radical Statistics [mailto:[log in to unmask]] On Behalf Of BYRNE D.S.
Sent: 16 August 2007 15:16
To: [log in to unmask]
Subject: Re: The holy grail?

 

This is all about simple complexity and may or may not be correct in relation to such simple complex systems. By a simple complex system I mean a system where emergence occurs solely as a result of interaction among the elements of the system. So for example if we look at a flock of starlings changes in flight pattern result from each bird observing very simple rules in relation to its neighbours but the whole flock generally makes quite complex changes of direction as one, although even here groups may split off. Another example is traffic jams, and Gawd help us all, perhaps financial markets.

 

The key issue would be identifying when a phase shift is about to occur. If there is a constant monitoring of information, or of course in reality a lot of repeated observations, across large numbers of cases, then we might see that point BUT that would seem to destroy the object of the whole exercise since we have to look at lots of cases to know when we can derive information from a few cases.   Financial markets might be an example because aggregate data is generated and can be tracked so monitoring some cases might be enough BUT since the cases would be human subjects as market makers the monitoring might change their behaviour.

 

Crowds are another matter and again how would you monitor - CCTV I suppose. So expect to have the  polises charge you on a demonstration because five people are moving  so as to trigger a response -  recipe for revolution perhaps?

 

David Byrne

 

From: email list for Radical Statistics on behalf of Paul Spicker
Sent: Mon 8/13/2007 1:12 PM
To: [log in to unmask]
Subject: The holy grail?

There is a remarkable claim in the "news" section of New Scientist this week, in a piece entitled "Predicting change, not a moment too soon".  A piece in Physical Review E (which I don't have access to: ref DOI: 10.1103/PhysRevE.75.051125) claims that changes in the behaviour of swarms, crowds, traffic jams or similar systems can be predicted by monitoring a very small number of particles.  "Using a mathematical model of a phase transition, they attempted to detect an oncoming change by monitoring only a small fraction of the elements in the system. They found that they could do so by focusing on the 'mutual information' shared by those elements. ...In a disordered state, looking at a particle gives no information about what others are doing.  As the system approaches a phase transformation, the mutual information betwen particles increases, so that one particle's behaviour does provide information about the speed and trajectory of other particles. ... The researcher's simulations suggest that in a crowd of, say, 1000 people, observations on as few as five people might be sufficient." 

I think it was George Gallup who suggested that it might be ultimately be possible to predict election results using five people. I'm not, sure, though, that I believe it.  If anyone's in a position to appraise the technique it would be fascinating to know about it.

Paul Spicker





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