Petter Holme

Emphasizing our focus on temporal networks, I am happy to announce that temporal networks czar,  Petter Holme will visit the lab on Feb 18th. Petter is the author (with Jari Saramäki, who visited last week) of the recent  & excellent review on temporal networks.

He will be giving giving an talk, and if you’re in the neighborhood, I highly recommend attending.

  • Speaker: Petter Holme. Associate Professor. Department of Energy Science. Sungkyunkwan University, Suwon Korea
  • Date. Feburary 18th, 2015
  • Time. 14:00
  • Location. DTU, Building 321, room 134
  • Title: Temporal networks of human interaction

Abstract: Since the turn of the millennium, networks have become a universal paradigm for simplifying large-scale complex systems, and for studying their system-wide functionalities. At the same time, there is considerable evidence that temporal structures, such as the burst-like behavior of human activity, affect dynamic systems on the network. These two lines of research come together in the study of temporal networks. Over the last five years, there has been a growing interest in how to analyze and model datasets in which we not only know which units interact (like in a traditional, static network), but also when the interactions take place. Just like static network analysis, the development of temporal network theory has been accelerated by the availability of new datasets. It should be noted that temporal networks are more than just extensions of static networks—they are e.g. (unlike simple, directed, weighted and multiplex networks) not transitive. In other words, if A and B are connected, and B and C are also connected, this does not imply that A and C are connected. Perhaps for this reason, temporal network theory has focused less on structural measures and studies of simple evolutionary models, and more on randomization studies and the simulation of spreading on empirical data. I will describe the state of the field, my own contributions (mostly about how temporal contact patterns affect infectious disease spreading), and discuss some future challenges.

Privacy Part II: Some examples of why privacy is important.

[This is part II of a series, you can find an overview here]

There are many reasons why privacy is important. I will not try to cover them all here, but instead I have chosen two central topics, which I find particularly important.

“I have nothing to hide, so why should I care?”

This one is a classic retort against privacy advocates. It has been used by Google’s then-CEO Eric Schmidt, who famously noted “If you have something that you don’t want anyone to know, maybe you shouldn’t be doing it in the first place” during a TV interview. And on the surface, it looks like a pretty good one (one that I might have used a few years ago).

Keeping private does not imply wrongdoing

There are many reasons why the nothing-to-hide stance is problematic. To me, the central reason is that it pre-supposes that things we want to keep private are “secrets”, the argument insinuates that a kind of wrongdoing is taking place whenever we want to keep something to ourselves.

But imagine that you have just found out you and your significant other are pregnant. Maybe that’s a piece of information that you would like to wait approximately 12 weeks before you share with the world? And maybe you would want to tell your close family before before announcing the news to a broader circle of friends? On a less cheery note, you might want to control how your surroundings learn about other big personal events, for example a serious disease, such as cancer. As another example consider someone who just fell in love. Not being able to control who knows about your deepest feelings could potentially be deeply embarrassing.

These are not exactly dark secrets – just personal issues. But something that most people can understand, why we’d like to keep private.

Personal freedom is restricted

More generally, a world where all of your actions are known to everyone, becomes a world where personal freedom is restricted. I feel like I’m already experiencing this on e.g. Facebook, it looks like many present a curated, version of reality to the world, focusing mostly on positive aspects of their life (think photos of cute kids + delicious meals), while ignoring moments of doubt and insecurity. On Twitter, I know that what I say is persistent, so I usually avoid saying anything negative. In writing this post, I searched for “US torture war on terror” on Google and wondered if that would put me on som kind of watch list.

Because there is a multitude of things that are completely legitimate, but that we might not want to share with everyone – we risk inhibiting ourselves whenever one of those topic come up in a “persistent medium”.  That also means that your freedom is particularly reduced if your personal preferences do not line up completely with main-stream social norms. For example, in a world where every action is know to everyone, young gay or transgender people might have a difficult time finding themselves (= even more difficult than now).

Nothing-to-hide and the government

“Trust is good, but control is better”, as Lenin probably said. If a government systematically collects data on its citizens, the nothing-to-hide discussion finds new nuances.

Private information can be used as a means of control (e.g. via blackmail). Now, if your opponent has lots of ressources as well as access to a powerful legal system, this type of control  is not limited to individuals with “something to hide”. There are some great quotes on this. Bruce Schneier points to  Cardinal Richelieu who said “If one would give me six lines written by the hand of the most honest man, I would find something in them to have him hanged.” The russian dissident Aleksandr Solzhenitsyn said “Everyone is guilty of something or has something to conceal. All one has to do is look hard enough to find what it is”.

I tend to trust my government, so I’m not too worried about being blackmailed. As a pretty main-stream person, that’s probably a good assessment of my situation. But what if you’re in a minority? The United States has tortured innocent people  as part of the war on terror. Homosexual acts were illegal in the UK until 1967, and it can be argued that racial segregation in the US persists in varying degrees to the present day. Additionally, much of the world is run by governments that are not democratic and whose choices and inner workings are not transparent to their citizens.

Finally, even if you truly feel like sharing everything, there is a strong argument that as a society we want some people to have secrets. We want a free press with journalists that can protect their sources. Protected sources give citizens access to parts of society that we can otherwise never access – the criminal world – or inside governments.

The future: loss of self

There is another argument for privacy. It’s a a little more out here, but still central to the debate. The essence of the argument is that data collected about individuals can be used for other kinds of control than simply using blackmail. The next level is individualized manipulation.

In order to get that part up and running, recall that there has been some very interesting developments in the behavioral science, such as cognitive psychology, social psychology, behavioral economy, etc. The term that embodies all of these developments is nudging. The general idea is that, during human evolution, our brain has developed to make very quick decisions in a world that looks very different from our modern surroundings. Because of the need for milli-second speed, many of our decisions are not based on rational chains of thought, but on built-in heuristics. If you have a few hours to kill, check out of this list of known cognitive biases. Nudging is essentially the practice of “hacking” these heuristics to manipulate human behavior – and can be used as a force for good (e.g. to recycle or promote saving for retirement) or in more questionable ways (e.g. to sell us stuff).

One can imagine that data mining of personal data can be used to create personalized nudges. This is already happening to some extent – for example people with macs are steered towards more expensive hotel rooms than windows users on some sites.

Clearly, humans have always been manipulating each other – just think back to last time you purchased a car. But algorithmic nudging is different. In part because it runs at scale, with a single company potentially reaching hundreds of millions of users, and in part because the nudging potentially can be much more precise and effective.

We’re not there yet, but the long term perspectives are terrifying. In a fascinating piece in the New York Times called “Privacy and the Threat to the Self“, the philosopher Michael P. Lynch makes the case that complete loss of privacy effectively dehumanizes us and takes away our “self”. He writes:

To get a sense of what I mean, imagine that I could telepathically read all your conscious and unconscious thoughts and feelings — I could know about them in as much detail as you know about them yourself — and further, that you could not, in any way, control my access. You don’t, in other words, share your thoughts with me; I take them. The power I would have over you would of course be immense. Not only could you not hide from me, I would know instantly a great amount about how the outside world affects you, what scares you, what makes you act in the ways you do.  And that means I could not only know what you think, I could to a large extent control what you do.

Here, Lynch – from another vantage point – discusses what we have covered above. The fact that knowing about people allow you to control them. But we begin to see that it’s not just about blackmail, but also about manipulation. That’s where the personalize nudging comes in. Knowing enough allows you to accurately “read people’s mind” or at least anticipate their actions. He continues to say:

That is the political worry about the loss of privacy: it threatens  a loss of freedom. And the worry, of course, is not merely theoretical. Targeted ad programs, like Google’s, which track your Internet searches for the purpose of sending you ads that reflect your interests can create deeply complex psychological profiles — especially when one conducts searches for emotional or personal advice information: Am I gay? What is terrorism? What is atheism? If the government or some entity should request the identity of the person making these searches for national security purposes, we’d be on the way to having a real-world version of our thought experiment.

In the second paragraph, Lynch discusses another point that I have touched upon above. Surveillance is already happening. And the quote contains nice examples of how our online behavior may reveal lots of information about us, which is private in the sense that we might not want to share with everyone, but not something which implies any kind of wrongdoing. The final paragraph goes into why all this implies a loss of self:

But the loss of privacy doesn’t just threaten political freedom. Return for a moment to our thought experiment where I telepathically know all your thoughts whether you like it or not From my perspective, the perspective of the knower — your existence as a distinct person would begin to shrink. Our relationship would be so lopsided that there might cease to be, at least to me, anything subjective about you. As I learn what reactions you will have to stimuli, why you do what you do, you will become like any other object to be manipulated. You would be, as we say, dehumanized.

If someone knows everything about you, and can manipulate you to their whim, you cease to be a human being. If that’s not scary, I don’t know what is.

Now, we’re still far from this scenario (last time I bought a pair of sunglasses on line, I encountered pointless ads for sunglasses on most sites for months after) . In fact, it’s not clear to me that we will ever get to the point where we can accurately make predictions on the actions of single human beings. [BTW another great article on the topic, from a more practical standpoint can be found here]. But I hope that I’ve made a case that privacy is something that is so important that we should all be discussing it.


Later this month, we’re lucky to have Jari Saramäki visiting and speaking at the lab. Jari is an expert on temporal networks (I highly recommend the excellent review paper on temporal networks that Jari co-authored with past and future guest of the lab, Petter Holme).

Jari is an associate professor at Aalto University and a highly cited author of many high impact papers on complex networks, for example:

  • Jari Saramäki, E. A. Leicht, Eduardo López, Sam G. B. Roberts, Felix Reed-Tsochas, and Robin I. M. Dunbar. Persistence of social signatures in human communication. PNAS 111 (3) 942-947 (2014).
  • Lauri Kovanen, Kimmo Kaski, János Kertész, and Jari Saramäki. Temporal motifs reveal homophily, gender-specific patterns, and group talk in call sequences. PNAS 110 (45) 18070-18075 (2013).
  • J.-P. Onnela, J. Saramäki, J. Hyvönen, G. Szabó, D. Lazer, K. Kaski, J. Kertész, and A.-L. Barabási. Structure and tie strengths in mobile communication networks. PNAS 104 (18) 7332-7336 (2007).

Below are the details of his talk.

From minutes to months: call network dynamics at multiple timescales

  • Date: 27th of January
  • Time: 14:00
  • Location: Auditorium 040 in DTU Building 324.

Abstract: Big Data on human interactions and communication have revolutionized the ways how human behaviour can be approached from a quantitative point of view. Mobile telephone Call Detail Records (CDR’s) have proven especially fruitful for understanding one-to-one communication patterns and the dynamics of inferred social networks. I will discuss what happens and when in call networks constructed from CDR’s with time stamps; this talk can be considered a mini-review of what we know about temporal networks of mobile telephone calls. I will begin with short timescales and fast dynamics (such as burstiness of sequences of calls between individuals) and “zoom out”, from temporal motifs formed of correlated calls between multiple individuals to long-term dynamics of personal networks of individuals.

Privacy Part I: Why everyone is complaining, but no one is taking action.

[This is part II of a series, you can find the overview here]

We all have a sense that privacy is important. A sense that our ability to freely express “who we are” is slowly eroded by large corporations and governments collecting data on our actions for purposes not clear to us (and maybe not to them either). But on the other hand, no one is doing anything about this. Why is that?

I think that there are two central reasons for this.

The first reason is that humans are not very good at handling situations where cause and effect is separated by a lots of time and space. (I was made aware of this point by an excellent column in the Guardian by the author Cory Doctorow, who I will be stealing from in the following). There are lots of examples of this: No one would smoke if you developed cancer immediately upon the first drag of a cigarette. The possibility of cancer is so far away in time that it feels like the consequences happen to another person. You would be less likely to  binge-eat if the food immediately was converted into belly flab.

Something similar is going on with privacy. You don’t immediately notice any problems when you hand over all of your email correspondence to Google or outsource your social network to Facebook, or signing up for free Airport Wifi. And it’s even worse because we don’t even know what the consequences of sharing those data might be. Figuring out what we can learn about individuals is an emerging field. And while we know that you can estimate e.g. your political views based on your Facebook feed, we’re still working out what it really is that you’re revealing about yourself, when you’re sharing data … and how those pieces of information can be used to manipulate you.

In fact, the entities that know most about what your personal data can be used for (e.g. Google, Facebook, Apple, Amazon), have very little incentive to share this information with the general public. In part because opening up can damage their public image (e.g. the Facebook mood experiment), and in part because sharing insights might run counter to shareholder interests (e.g. making tons of $$$ manipulating people) [1]. This is why the kind of research that we do here at DTU is so important – providing a public and open counterpoint to large corporation with private research divisions.

The second (and even more important) reason is that it is not at all clear what kind of action we should take. Privacy is such a complex issue that even if you want to take action, there is no obvious path to follow. To make such a path a little bit clearer is, my goal with the posts in this series. I’ll try to find a little bit of solid ground so that maybe we’ll have something to mobilize around once we feel like it’s time to take action.


[1] Thanks to Piotr Sapiezynski for making this point.

Some thoughts on privacy. Part 0

Recently I’ve been thinking a lot about privacy.

My own work focuses on what we can learn from dense data collected by volunteers at my university (DTU), and that means that privacy is something I think about a lot. What we’re learning from our amazing dataset shows that data channels are highly overlapping and even something like which WiFi access points your phone sees (sounds innocuous, right?) reveals pretty much everything about both your movement around in space as well as your social connections.

Because or our findings, I am concerned, for example, by the City of Copenhagen’s decision to monitor everyone in the city using WiFi routers. It’s not trivial to me that it is OK for the city to perform this kind of monitoring. More generally, the further we move into a future, where we haven’t set down simple ground rules for what’s OK and what is not OK, the more difficult it will be to find our way again.

Overall, however, I think sharing data is a great idea and usually data-sharing is a win-win proposition. But we have to make sure that we have rules that ensures the right balance of power between individuals and the entities that use their data.

Inspired by Clive Thompson’s thoughts on public thinking, I’ve decided to write a few posts about privacy and data on this blog even though I haven’t really figured out what to think about all aspects of the topic yet.

Thus, in the coming weeks (probably months, knowing my tendency to procrastinate), I’ll be writing about privacy here. A tentative outline of the series is:

  • Part I: Why everyone is complaining, but no one is taking action.
  • Part II: Some examples of why privacy is important.
  • Part III: Why technical solutions will not work.
  • Part IV: Suggestion for simple rules for data.
  • Part V: Sharing and electronic traces present an even deeper problem. I’ll present a sketch of a solution.
  • Part VI: Why all this does not mean you should not share your data. It’s generally a great idea to share with data both corporations and governments. Maybe also something about why companies with reasonable data policies will have a competitive advantage.

Talks next weeks

It’s not just the network structure that we care about. We want to understand network structure in order to get a handle on processes taking place on networks. That kind of processes is what next week’s two exciting (Monday and Tuesday October 6th and 7th, at 11am @ DTU) talks focus on. Both talks are open to the public, so I hope you’ll join us if you’re in Copenhagen. Full details here:

Cornelia Betsch on Vaccination Decision Making

  • Time: Monday, October 6th, 2014
  • Place: Technical University of Denmark, Building 321, 1st floor Lab Space
  • Title: Vaccination decision making – an individual and social perspective
  • Speaker: Dr. Cornelia Betsch. PD Dr. Cornelia Betsch is research fellow (Akademische Oberrätin) and scientific manager of the Center for Empirical Research in Economics and Behavioral Science (CEREB) at the University of Erfurt, Germany. She serves as a member of the European Technical Advisory Group of Experts on Immunization (ETAGE) of the WHO Europe and as a member of the German Commission for the Verification of Measles and Rubella Elimination(Federal Ministry of Health @ Robert Koch Institute).
  • Abstract: The desperate search for a vaccine against Ebola currently reminds us on the merits and value of vaccination. Still, there is a small but critical amount of parents and adults who decide not to vaccinate their children or themselves. They endanger public health goals such as the elimination of diseases like measles or polio. In this talk I will show from the individual perspective what may influence a decision against vaccination. Further, I will analyze the vaccination decision from a structural point of view and show the social perspective of vaccination decision making: as many vaccinated individuals can protect some unvaccinated individuals, it may be rational to forego vaccination and to free ride. Given we know something about how people make vaccination decisions, which strategies should we choose for vaccine advocacy? In the final part of the talk I will give some examples and link them to real-world challenges of vaccine communication.

Jens Koed on Describing the psychology of argumentation

  • Time: Tuesday, October 7th, 2014
  • Place: Technical University of Denmark, Building 321, 1st floor Lab Space
  • Title: Describing the psychology of argumentation, reasoning, and persuasion from a Bayesian perspective
  • Speaker: Jens Koed Madsen (Postdoc @ Birkbeck, University of London)
  • Abstract: Classical psychological models of persuasion and reasoning (Chaiken, 1980; Petty & Cacioppo, 1981) conceptualise rationality from the perspective of formal logical reasoning. Empirically, however, humans do not respond in line with logical predictions, as many fallacious arguments are accepted, and not all valid arguments are accepted. This has led to the conclusion that humans are not rational and to the development of the dual-process theory (consisting of a slow, laboured, and logical and a shallow, heuristic, and non-logical system). Recently, rationality has been recast as reasoning from uncertainty rather than reasoning from certainty from a Bayesian perspective (Oaksford & Chater, 2007). The paradigm has successfully been applied to reasoning (e.g. Oaksford & Chater, 2007), argumentation (e.g. Hahn & Oaksford, 2006; 2007), fallacies (e.g. Corner et al., 2011; Harris et al., 2012), persuasion (Madsen, 2013), and has integrated source credibility in a reasoning framework (Hahn et al., 2009; Harris et al., submitted). I work on three aspects of Bayesian persuasion: the conceptual development of the persuasion model from the thesis (Madsen, 2013), the psychological ontogenesis of probabilistic estimations, and the relationship between individualised approaches to belief changes and behaviour changes. These aspects touch upon the modelling, theoretical foundation, and application of the Bayesian approach developed in the past decade.

Bibliography for Jens’ talk

Chaiken, S. (1980) Heuristic versus systematic information processing and the use of source versus message cues in persuasion, Journal of Personality andSocial Psychology 39, 752-766

Corner, A., Hahn, U. & Oaksford, M. (2011). The psychological mechanism of the slippery slope argument. Journal of Memory & Language, 64, 133-152.

Hahn, U., Harris, A. J. L., & Corner, A. (2009). Argument content and argument source: An exploration. Informal Logic, 29, 337-367.

Hahn, U. & Oaksford, M. (2006a) A Bayesian Approach to Informal Reasoning Fallacies. Synthese 152, 207-23

Hahn, U., & Oaksford, M. (2007a) The rationality of informal argumentation: A Bayesian approach to reasoning fallacies, Psychological Review 114, 704-732

Hahn, U., Oaksford, M., & Harris, A. J. L. (2012). Testimony and argument: A Bayesian perspective. In F. Zenker (Ed.), Bayesian Argumentation (pp. 15-38). Dordrecht: Springer.

Harris, A. J. L., Hahn, U., Madsen, J. K. & Hsu, A. S. (submitted) The Appeal to Expert Opinion: Quantitative support for a Bayesian Network Approach, Cognitive Science, XXX, xxx-xxx

Madsen, J. K. (2013) Prolegomena to a Theory and Model of Persuasion Processing: A Subjective-Probabilistic Interactive Model of Persuasion (SPIMP), unpublished thesis, University College London

Oaksford, M. & Chater, N. (2007) Bayesian Rationality: The probabilistic approach to human reasoning. Oxford, UK: Oxford University Press.

Petty, R. E. & Cacioppo, J. T. (1981) Attitudes and persuasion: Classic and contemporary approaches, Boulder, CO: Westview Press

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