Spatial Transmission Models: A Taxonomy and Framework

This paper , in press in the journal Risk Analysis, sets out a review of the different methods used for modelling the spread of an idea, disease, etc. over space.

ABSTRACT

Within risk analysis and more broadly, the decision behind the choice of which modelling technique to use to study the spread of disease, epidemics, fires, technology, rumors, or more generally spatial dynamics, is not well documented.

While individual models are well defined and the modeling techniques are well understood by practitioners, there is little deliberate choice made as to the type of model to be used, with modelers using techniques that are well accepted in the field, sometimes with little thought as to whether alternative modelling techniques could or should be used.

In this paper, we divide modelling techniques for spatial transmission into four main categories: population-level models, where a macro-level estimate of the infected population is required; cellular models, where the transmission takes place between connected domains, but is restricted to a fixed topology of neighboring cells; network models, where host-to-host transmission routes are modelled, either as planar spatial graphs or where short cuts can take place as in social networks; and finally agent-based models which model the local transmission between agents, either as host-to-host geographical contacts, or by modelling the movement of the disease vector, with dynamic movement of hosts and vectors possible, on a Euclidian space or a more complex space deformed by the existence of information about the topology of the landscape using GIS techniques. We summarize these techniques by introducing a taxonomy classifying these modeling approaches.

Finally, we present a framework for choosing the most appropriate spatial modelling method, highlighting the links between seemingly disparate methodologies, bearing in mind that the choice of technique rests with the subject expert.

A YouTube Reading List for Practitioners and Students of Management

One of the issues with strategic management (and business management more generally) is that the folklore of academic writing is passed down the generation, from professor to student, without a critical reading of the original works, or without a read at all.

Business text books excerpt the salient points from academic articles, and can miss the nuances of the text.

At Oxford, students are required to read 10-20 articles per week which they synthesize into a tutorial essay.

Some of us do not have the luxury of being able to study for a degree full time, and may not have access to the original articles – although sites such as Google Scholar and ResearchGate are starting to break down the barriers to access to academic works.

I am starting a series of YouTube videos to cover a relatively broad area – general management, strategic management, and other bits and pieces that I find interesting.

I will upload these to my YouTube channel.  I hope you find them interesting.  Please do leave comments on the video’s page on YouTube, and consider subscribing to my channel for a (hopefully) regular dose of academic articles to keep you thinking about management a little more critically.

PhD Studentship in Modelling Dynamic Responses to Dynamic Threats at Loughborough University

I am co-supervising the following PhD project – the application link and further details can be found here: http://www.lboro.ac.uk/study/postgraduate/research-degrees/funded/modelling-dynamic-responses/ .  The closing date is 14 December 2017.  Please get in touch if you would like to discuss this opportunity.

One of the most challenging issues for policy makers dealing with bio-security threats is their dynamic nature: diseases may spread quickly and deadly among vulnerable populations and pandemics may cause many casualties.

Finding the appropriate response to threats is a major challenge. Whilst models exist for understanding of the dynamics of the threats themselves, responses can be largely ad-hoc or ‘firefighting’. The aim of this research is to produce robust responses for dynamic threats.

The research will build up as follows, from low to high complexity: static responses to static threats; static responses to dynamic threats; dynamic responses to static threats; and dynamic responses to dynamic threats.

We will use a variety of methods to define the best response: cellular automata, network analysis, spatial modelling, agent-based modelling, and the generation of dynamic fitness landscapes.

This PhD studentship is most suitable for candidates with a background in a quantitative discipline such as management science, operations research, engineering, physics and other natural sciences.

Why The Mayor of Houston Was Right to Not Evacuate the City

Right now, Houston is going through one of the most severe storms ever to hit the USA.  The main conversation on today’s news was whether the Mayor (who has authority to do such things) should have evacuated the City prior to the arrival of Hurricane Harvey.

For a start, NOAA did not forecast a direct hit on the City.  But it was forecast that potentially devastating rains were on the way.

Houston has been here before, of course, in 2005 when the then Mayor did order that the city be evacuated.  And around 100 died, as a result of the gridlock and heat.

But let’s think about what an uncontrolled evacuation of Houston would mean.

This is the map of the Houston highway system.

And here is is on Google maps.

 

While there is, of course, a Houston evacuation plan, assuming you want to avoid the Gulf of Mexico, the main routes are via the north and west: I69 to the north-east, I45 to the north, US Route 290 to the north-west, and I10 to the west.

Now let’s consider the capacity of these roads.  The capacity of roads in the US is given by the Department of Transportation’s Highway Capacity Manual.  While there is a whole science devoted to calculating freeway flow measurements, you need to take into account not only the capacity of the road (the number of cars), but also their speed.  Combining these gives us a flow rate, i.e. the number of cars that will pass a point in a particular length of time.  We can look at the academic literature to see what this is.  Dixit and Wolshon (2014) have a nice study where they looked at maximum evacuation flow rates.  Their Table 2 shows the empirical data, but it’s around 1,000 vehicles per hour per lane.  Assuming the Houston metro system evacuation routes of the north and west are around 4 x 4 lanes.  Give a factor of 1.5 for contraflows, and you have around 25 lanes.  So that’s 25 x 1000 = 25,000 vehicles per hour.  And let’s assume an occupancy of 4 passengers per vehicle (i.e. most would evacuate by car).  So that’s 100,000 passengers per hour.

The problem with Houston is that it’s the USA’s fourth largest city.  And that means it’s big.  It (Greater Houston) has a population of 6.5 million.  So that means 6.5 million / 100,000 = 65 hours.  Non stop, day and night.  Without accidents.  A very bold move for a hurricane that was not due to hit directly.

And tropical storm watches are only typically issued 48 hours before winds are due to strike.

By not evacuating, resources are kept in Houston rather than being disseminated across the locations of incidents caused by evacuating traffic.

The real test however comes in the days and months ahead, where the process of rescue, recovery, and rebuilding is critical.

References

Dixit, V. and Wolshon, B. (2014) ‘Evacuation Traffic Dynamics’, Transportation Research Part C, 49, 114-125

 

The Most Competitive Airline Routes in the World

I am using airline data to construct a network of competition in the airline industry.  As part of this, I am listing the routes that are the most competitive – not necessarily the ones that have the most flights, but the ones that have the most competitors.

And here they are

Map generated from GCMap.com

HKG-ICN  Hong Kong – Incheon, Seoul (South Korea)

Not shown: EastarJet

TPE-NRT  Taipei (Taiwan) – Narita, Tokyo (Japan)

Not shown: Vanilla Air, Tiger Air, Scoot, Transasia

SIN-CGK   Singapore – Jakarta (Indonesia)

Not shown: Indonesian Air Asia, Scoot, JetStar Asia

SIN-DPS   Singapore – Denpasar, Bali (Indonesia)

Not shown: Qantas, Qatar, Indonesia Air Asia, Scoot (nb JetStar and JetStar Asia are different airlines)

Please note that these data are a few years old, are preliminary and not completely accurate, and airlines come and go on such competitive routes.

Two Funded PhD Studentships in Agent-Based Modelling at Loughborough University School of Business and Economics

I am looking for high quality, numerate, candidates to fill these exciting PhD studentships with me as a (co-) supervisor at Loughborough’s School of Business and Economics.  Please note that this post has been updated with new links (in blue, below).

The first is modelling dynamic responses to dynamic threats; the second is using analytics in traditional industries.  Please see the links below for further details and how to apply.  Note that for further information, you will need to click on the blue links below.

Modelling Dynamic Responses to Dynamic Threats (with Professor Gilberto Montibeller)

One of the most challenging issues for policy makers dealing with bio-security threats is their dynamic nature: diseases may spread quickly and deadly among vulnerable populations and pandemics may cause many casualties.

Finding the appropriate response to threats is a major challenge.  Whilst models exist for understanding of the dynamics of the threats themselves, responses can be largely ad-hoc or ‘firefighting’.  The aim of this research is to produce robust responses for dynamic threats.

The research will build up as follows, from low to high complexity: static responses to static threats; static responses to dynamic threats; dynamic responses to static threats; and dynamic responses to dynamic threats.

We will use a variety of methods to define the best response: cellular automata, network analysis, spatial modelling, agent-based modelling, and the generation of dynamic fitness landscapes.

This PhD studentship is most suitable for candidates with a background in a quantitative discipline such as management science, operations research, engineering, physics and other natural sciences.

Business Analytics for Public Services and Regulated Industries: New Techniques for Analytics-Driven Decision Making in Traditional Industries (with Dr Maria Neiswand and Professor David Saal)

The rise of business analytics has given rise to enormous opportunities within the private sector, but these benefits have yet to be fully realized in public services and regulated industries such as energy, water, and transportation networks. Conversely, governments are mandating collection of data by installing smart metering devices. This gives rise to the need for innovative ways of thinking in industries that are still largely based on traditional economic thinking involving conventional assumptions on optimization and behaviour.

As an example, the energy sector is characterised by strongly defined market structures with incumbents and an ultimate need for energy network security, which not only prevents the quick adoption of technical changes but also translates into regulatory outcomes, such as price caps.

This exciting PhD opportunity will integrate theoretical and empirical approaches and spans two strengths of Loughborough’s School of Business and Economics: microeconomics and particularly rigorous analysis of the determinants of productivity and performance (including cost modelling) and management science (including simulation and network analysis).

We are therefore seeking a student with a quantitative background (whether in economics, management science, engineering, physics or other natural sciences). A willingness to learn new techniques such as, cost modelling, performance measurement, agent-based modelling and network analysis is desired.

 

Accessing Academic Journal Articles when away from a University

Now is the time when students, and indeed academics, are away from universities.  From having academic journal articles at your fingertips, you can find yourself confronted by previously good natured academic publishers persuading you to part with your hard earned cash in order to access an article.

This is not a good thing.

So, from hardest to easiest, here are methods for accessing those articles.  This is for the University of Oxford, but other universities have the same setup.

University Library Journal Search

For example http://www.bodleian.ox.ac.uk/ptfl/eresources/ejournals

Various journals have various sign in mechanisms, which is a bit of a pain, but you probably will be able to find what you are looking for here.

VPN

Many journals are accessible when connected within your university – access tends to be based on the IP address of your computer.  So, no access from outside.  To counter this, you can use a VPN – for example http://help.it.ox.ac.uk/network/vpn/index – you need to download VPN client software, and that should make it seem as though your computer is in Oxford, and you should have access.

Google Scholar

The other way of doing it is to search for the article title in Google Scholar.  See for example https://scholar.google.co.uk/scholar?hl=en&q=Agent-Based+Models+and+Behavioral+Operations+Research&btnG=&as_sdt=1%2C5&as_sdtp= . The pdf link on the right should give you access.  If that doesn’t work, you can sometimes find the right version by clicking on ‘All n versions’, as one of those may be the pdf.

Google

And if that doesn’t work, just Google the name of the article followed by filetype:pdf, for example https://www.google.co.uk/search?site=&source=hp&q=Agent-Based+Models+and+Behavioral+Operations+Research+filetype%3Apdf&oq=Agent-Based+Models+and+Behavioral+Operations+Research+filetype%3Apdf

Appeal to the Author’s Vanity

And if that all fails, write to the author(s) directly.  We are vain people, and there’s nothing better than to receive a request from a student, particularly if they are genuinely interested in the work.  Just type their name into Google, and their university webpage should show you their contact email address.

Agent-Based Models for Simulating Human Behavior: IFORS Conference 2017

This presentation including joint work with Alberto Franco, was presented at the IFORS (International Federation of Operational Research Societies) conference in Quebec City, QC, Canada.  We present two different agent-based models for simulating human behavior.

We use the example of group decision making.

The first model uses a cognitive fitness landscape to model the quality of a decision, where participants compare their decision with their nearest neighbor.  The decision is based on an external comparison.

The second model uses an internal comparison of a decision with the next best alternative.  The model is based on the psychological concept of hidden profiles, where participants only make the best decision by sharing information with the group.

The Conservative Manifesto: Care Fees as a Percentage of Initial Wealth

The Conservative Party have announced their manifesto for the 2017 General Election.  Included in this (on page 64-65) is proposed

We will introduce a single capital floor, set at £100,000, more than four times the current means test threshold. This will ensure that, no matter how large the cost of care turns out to be, people will always retain at least £100,000 of their savings and assets, including value in the family home.

A quick calculation on the effective ‘Tax’ (Care Fees as a Percentage of Initial Wealth) shows the following distribution of Tax Rates.  On the x axis is initial wealth (the value of your house plus any savings), and on the y axis is the Tax Rate.  The Conservative Party have since augmented this plan with a proposed cap (consultation to come).

Values used for Care Fees: £20,000, £40,000, £60,000, £80,000; £100,000.  Values used for Initial Wealth: £0, £100,000, …, £1,000,000.  The trend continues downwards after this figure.

As many have pointed out, this affects individuals with initial wealth just over £100,000 proportionately far more than those with higher initial wealth.  More detail on policy options for funding social care can be found in the Dilnot Commission report and a summary of their proposals is shown below: