Tag Archives: complex network

[Conference Report] Experiments in Social Networks

Fortunately, I went to two conferences in the past month, one specialized academic conference on Complex Network held by University of Electronic Science and Technology of China, and the second one was organized by my dear UseR friends and I, which was the 4th China-R Conference (Shanghai) in East China Normal University.

It was really my honor to participate in these two conferences and deliver presentations to the audience. My talk was focused on experiments in social networks, and some consequent analysis in R. As the conferences were in China, I talked in Chinese throughout. Social network is a hot topic nowadays, but experimental methods are still at the beginning stage. With social learning models, we found out a good way to test the network effects with randomized experiments.

It was also my great pleasure to meet famous scholars worldwide. In the complex network conference, a lot people from physics and computer science brought my with fresh knowledge and inspirations. In the R conference, we invited so many experienced useR and exchanged our experience of using R. It is always good to feel that many people are enjoying the convenience of R and are happy to play with data in numerous fields.

At last, here are the slides I used to assist my presentation. Sorry but they are in Chinese...



Physics > complex network > link prediction

It is a little funny that while I was trying to build the psychological-economic model in partner matching, two papers appeared in front of me, and they are all about link prediction:

  • Linyuan Lu y Tao Zhou, “Link Prediction in Complex Networks: A Survey,” 1010.0725 (Octubre 4, 2010), http://arxiv.org/abs/1010.0725.
  • D. Liben-Nowell y J. Kleinberg, “The link-prediction problem for social networks,” Journal of the American Society for Information Science and Technology 58, no. 7 (2007): 1019-1031.

Nowadays as an economics student, one important thing you can never overlook is math. That is why sometimes I feel that I am paying more attention to math instead of those economic thoughts. Yes we always stress economic intuitions. However, when it comes to the time problem, apparently math training acquires more time. More important, you may not able to build the entire economic intuition system only through lectures. Outside of the classroom is the place where you can really recognize the sense of how economics is related to people’s everyday life. Newspapers, street talks, and even TV shows may be more helpful.

Well… a little off topic. Today when I was listening to Thijs, suddenly a question not relative to any materials from that course came to my mind. What do we really care? Explanation, or prediction power? Of course they cannot be separated with each other. However, when it comes to prediction, it seems that people care more about the accuracy instead of why this or that method is working well. The best example may be the variety of methods of stock prices predicting. Once when I attended a statistics conference, there was someone who talked about his beautiful “triangle” prediction model of stock prices. For me, it does not make any sense. First, I’m not in the stock market, so I do not care; second, this kind of prediction methods are built above the cloud – there is no foundations which can even partly support the logic beyond the seemly accurate results. It may be unfair to attribute those meaningless methods to physicians – however, more of them studied physics before and they are somehow trying to transplant those solid physical theorems to economics, regardless the fact that economics is a branch of social science, which studies the (economic) functions of the society, the interactions among people and the fundamental reasons behind human behaviors. That is why whenever I see any model directly related to physics, I’m more careful about the economic implications behind the model: at least it should not be contra-intuitive.

Now myself is trying to borrow something from physics…. Obviously the first rule for me it to be as cautious as I can. In particular, I am trying to apply the link prediction idea to economic and social network analysis. Somewhat like the debate about reduced form and structural form in econometrics, I do not want to lose the micro foundations and economic intuitions behind the fancy model itself. It is easier if I just want to predict the result, but with consideration of internal and external validity, the model should be granted with more explanation power, which can conquer the difficulties originated from the complexity of the real society. Actually, I am fond of the name of this branch of science – complex network. How can we abstract simplicity from the complicated world? That may be the common question confronted by every single branch of science, no matter social science or hard/natural science. Without idea experiments in social science, how far can we go? It is really a difficult question to answer….

Anyway, hopefully I can find out a way to introduce link prediction ideas to my naive economic model. It is always interesting to work on the boundary of two different fileds, and you are tasting something new. However, the exams are coming so fast... need to focus on reviewing first.... Will update more later.

the week of seminars

This week was pretty busy: seminars, my own presentation and of course, problem sets, and especially, Chinese New Year.... Well, it worth a brief summary.

Seminars began from the past Tuesday: I skipped the boring advanced macro class and went to the labor seminar series. The presentation was:

Alessandro Tarozzi (Duke University)
"Micro-loars, Insecticide-treated Bednets and Malaria: Evidence from a Randomized Controlled Trial in Orissa (India)"

Due to the reason that I may need to work on a public health/ health econ topic joint with a classmate as the final master project, I have to learn more about what they are doing in health econ. Although the presented paper was from an applied/metrics view, it was still interesting to see what problems they had met in the field works...

Another seminar was one of the recruiting one, offered by:

Speaker:    Konrad Burchardi (London school of Economics)
Title:    The Economic Impact of Social Ties: Evidence from German Reunification (with T. A. Hassan)

I should admit that I have been always curious about the job market papers: they can be downloaded from the Internet, and well-packed. How incentive compatiable they are! Moreover, I do care about this topic: social ties.... well, it was so sad that when he talked about the German history, I knew nothing and was quite confused with the process which he did not need to explain too much to other audience....my poor storage of European history knowledge! To be honest, during the seminar, I was wondering one thing: is he reading EJMR as well? From the forum, they are discussing this year's job market hotly, so there is a big chance that some of the speakers may also be a part of the readers/contributors. Woo, that would be an intersting question if their true types have been finally revealed by linking the real person with the online IDs....

Actually, just before the recruiting seminar, I gave my first (academic) presentation in class. Since it was the first time for me to present in front of a group of Ph.Ds and totally in English, I felt quite stressful  before the presentation. But it went much better than I had expected. I was pretty impressed by the active classmates - they were so kind and offered valueable comments. It automatically reminded me of the previous experience when I presented something in my undergraduate school. Nobody really cared about what I was researching. Fine... Such a sharp contrast. Maybe it is exactly the reason why that many talent researchers need to go outside of China and receive more advanced education in world leading universities: not only for the knowledge itself, but also with consideration of the environment, the people who they are going to work with. It is also exciting for me to see that our draft is growing mature and meaningful. At least, a very good and precious practice for me.

Another interesting episode:  after the seminar, I was walking with several classmates, and then we met our dear director Ciccone. He smiled to us, and suddenly said "that is impressive that you econ students  have time for seminars"... Well, yes we are pretty busy, but, I love seminars.... irreplaceable by normal lectures.

Now, I am at UAB, for the reason that today here is a workshop on network topics:

MOVE Meeting: Coalition Theory Network Workshop (16th Edition)

They have got numerous interesting papers, like

Kalyan Chatterjee:    "Word of Mouth Advertising, Credibility and Learning in Networks" (with Bhaskar Dutta)

Agnieszka Rusinowska:    "Iterating influence between players in a social network"

However, I was so tired and lazy this morning and I missed the first one... Actually, most of the papers are highly techinical, and I am not really interested in the technical tools they have used/developed in their papers. I care more about how they have applied the complex network theory to economic analysis and what they are paying attention to nowadays.

Ok. I think this summary is enough. Great week by any means. On the Chinese New Year's Eve I made dumplings for a few friends, mainly Chinese. Eh... Later tonight I need to make dumplings by hand again for my dear non-Chinese friends. Haha. Nice night awaits!

Social behavior VS Individual behavior

Well, recently I'm focusing on an interesting model --social network and thinking about an old issue --social behavior. The social network model is really attractive (if it can be regarded as a model, or more exactly, a theory), especially for people like me who are wondering the traditional assumptions in classical economics while trying to borrow something from other subjects, like sociology.

Using complex network as a mathematical tool, the social network model includes so many factors that cannot be described in the past. Well, I should admit here that I haven't taken any related courses yet, and all I know about sociology are inherited from some unprofessional books. I should also admit that I was really attracted by behavior economics last winter, but until now had I started to "study" it in an academic way. Maybe the reasons are pretty simple: first, I was busying applying for postgraduate study positions last winter; second, there was not a good teacher who was able to teach this course; third, I have no idea about which book (or textbook) should be chosen as an introductory one.

Well, I need some time to make it clear in my mind that how social network works. However,  I've got a much easier question yet. That is, in traditional macroeconomic models, like the Lucas' island model, when we are trying to calculate the sum of all individual's save, at most time we simply add them together, (i.e. a*N, where N is the number of population).  However, I think at least the individual's save should be regarded as a stochastic variable (e.g follows a normal distribution, or Brownian movement), so the sum should also follow a normal distribution. Well, in econometrics we do not need to worry about this question. But I wonder whether it would be valuable if we can make this small change.

In the example above, I want to figure out that the micro-foundations for macroeconomics should be dug more deeply in order to persuade readers.  Borrowing some mature conclusions from other fields, this task shall be easier. Alternatively, economists should make an effort (maybe something can be found from data) to know more about the relationships between individual behavior and social behaviors, thereby establishing a proper model to describe them. Personally speaking, the study of social network may be helpful, since different from other social science, at least it has a mathematical model...And the diffusion of information can be easily introduced into macroeconomic models in this way...WoW!