Network Theory

Been reading some books around network theory. The science of networks is interesting and applicable to many areas of society, organisations and nature. How do networks interact between fellow group members and between a closely linked network and a more distant one. How do diseases spread or not spread and how do they persist. Why do some products become a success and spread whereas others that seem equally valid disappear without trace.
Can you design a system to withstand attack more effectively. If you design it to resist the disruption of a major hub does that reduce its ability to cope with the loss of many smaller nodes. What patterns of distribution in sizes and density of links occur naturally in systems.
If we had a more complete understanding of how complex systems interact over time we could design more effective solutions to these real world problems.

How do diseases epidemics spread or not spread and how do they persist.

For a disease to spread it only needs to infect more than one neighbour before it kills its hosts or is killed.
If it can infect more hosts and lasts longer before it is killed off or its host is killed off then the disease has a better chance of spreading.
A disease that kills off its hosts very quickly can restrict its ability to spread as it kills off potential spreaders too quickly. A disease that is comparatively benign may persist a lot longer.
Its an interesting field to look at as an effective way of slowing the spread of diseases may not to be to look at the most connected person in the community but the marginal people who move between multiple groups and have more widespread connections as they are more likely to speed up the spread of the epidemic. A few people with longer distance ties may spread the disease much more quickly as they have the potential to infect many separate groups and are less likely to infect the already infected. As most peoples connections will be closer.

How best to design a system to withstand attack

If you can understand the structure of a network and how its nodes interact then it can help you make it more resilient. Duncan Watts talks about the structure of the Toyotas suppliers that allowed it to recover very quickly from the over night burning down of the major brake valve supplier. How the the other supplier companies rapidly adapted to producing valves they had never manufactured before.

You can see that if you have redundancy of telephone exchanges or power stations then the system as a whole can cope with one disappearing. But there is also the homogeneity of the population, if the many parts of the system all have a similar way of working or methods then the chances of them all being affected by the same adverse event are greatly increased. If ten banks all have the same sort of business model or use the same approach to estimating risks they are more likely to be affected by the same issues leading to system wide crisis rather than an individual bank crisis. This may however be counter intuitive, the vast majority of the time organisations tend to converge on what seems the most effective strategy for their competitors. If company A is using approach X and they are making 10% more profits its difficult for company B to see that their own strategy will cope much better with the crisis that will affect company A in two years time. They just see now and copy strategy X rather than see that if they had kept their original strategy they would be unaffected by the crisis that eventually blew up company A.
They have to be quite rational and long term and avoid the consensus but thats not how people and organisations naturally think.

Spiral of silence

This was an idea of Elisabeth Noelle-Neumann, a german political scientist and opinion pollster. If many of the people in a group profess on opinion, say as recently in the Scotland on leaving the UK. Then that can affect the opinions expressed by others, people are affected by what they perceive to be public opinion and moderate their expressed views to match. If you believe that everybody else is going to vote for Scotland leaving the UK, you are less likely to express your contrary opinion in public, which may help explain inaccuracy in recent election polling.
It may also have implications for political campaigns, if a member of the public can be convinced that the vast majority of the public are going to vote for candidate A then it may reduce the likelihood of them turning out for a alternative candidate or make then doubt their own decision. Most people fear isolation from the group. This can become self perpetuating.


Its interesting how little of this understood. It doesn’t seem that there are any absolute answers just more or less precisely fitting models and approximations. It seems like as with weather forecasting it gets beyond a certain point in the future and the system or group becomes too complicated to predict. Part of which seems to be because we don’t have the Maths.

There are lots of applications to this how best to design a social network, or an advertising campaign to spread quickly the optimum linking and grouping structure to aid the spread of ideas or in the case of diseases isolate or restrict transmission as much as possible. Many close links with occasional distant links between clusters may be more effective at spreading some thing than many things very closely linked as that is a inherently more stable structure with stronger links which harder to change.

Its an interesting set of things to read about though and definitely some food for thought.