Hello and welcome back to networks illustrated principles without calculus. In this lecture, were going to answer the question, how are people influenced on Facebook and Twitter? If you remember back to the lecture in which we talkede about viralization on YouTube, we were looking at everything as occurring at the population level. So, presumably anybody in the population could influence anybody else in the population. What we're really going to focus on in this lecture, is instead of population dependent models, we're going to look at topology dependent. Topology, dependant, models. And in doing so, we're going to leverage the social graph, amongst users. [SOUND] So a good segway from the lecture on YouTube into this lecture would be to say what now we understand some of the mechanisms of me going into making a video viral such as triggering information cascade. If we wanted to seed someone on Facebook or Twitter in order to maximize the chance that such an information cascade would happen, which people would we choose? And that's what we're going to look at in this lecture, is how we can use this social graph to see who is more important, and who would have a better chance of being able to trigger those things. Again, the underlying principle is going to be that crowds are not so wise. Because we're going to see that the opinions, in many cases amongst people are dependent rather than independent as we looked at in the case of the Amazon and Netflix with the wisdom of crowds. So by far the largest social networking site today is Facebook, which we all know and love. So lets take the next little bit to look at some background behind Facebook. Starting with, timeline of some early events that happened. So, though Facebook wasn't formally founded until mid 2004. it, it's roots can be traced back to January of that same year. When thefacebook was created for Harvard students by a then Harvard student Mark Zuckerberg. And this had been spired by one he had previously created which is called Facemesh. So, initially, it was restricted to only students at Harvard, but the site quickly attracted more than half of undergraduate population there. And, within less than two months it was already expanding to other schools. First Ivy League schools but, gradually, gain the attention of most universities in both the U.S. and Canada. And this time, remember, it was still restricted to college students only. Since 2005, it officially changed its name to Facebook and purchased the domain, Facebook.com. They went initially, as we said, it was The, The Facebook and now it's just Facebook. Even though there's not more than one, and around this time it was started to open up with high school students and then employees of certain companies. So, as we said, initially Facebook was for college students, but maybe around the 2005 time it started opening with the high school students and also employees. [BLANK_AUDIO] And then in September 2006 it finally opened up to everyone who's 13 and older and had a valid email address, which is the way that it has remained to the current day. So present through a wide range of demographics, Facebook has become almost ubiquitous in today's society. And as we said, it is the largest social networking site today. And this graph right here shows the evolution in the number of Facebook users by year from 2004, to the present. 2008 it hit 100 million users worldwide, right here in hits 100 million, this is in millions, so you can add an m next to each of these numbers. And once we get 1000 millions, that's just the same thing as 1 billion. And by 2012, it had hit that 1 billion mark. And so this, this, this range of time here, 2008, 2009, 2010, 2011 was the largest growth of Facebook in terms of absolute numbers, at least. And in that same year of 2012 Facebook had its IPO, which is its Initial Public Offering. And the company was priced $104 billion for that, which is the highest evaluation to date of any newly public company. And though the US has more than double the number of Facebook users than any other country, at least as of February of 2013, there's actually over 160 million registered, so there's 160 million from the US alone registered to Facebook. That's greater two times any other country. Facebook has a very broad international foothold. It has tens of millions from other countries. At least like Brazil and India at this time it was about 60 million each. Many links and connections have been formed among people using Facebook. So consider, suppose we took all the users on Facebook and represented them as nodes in a graph. So if we took every single user, and represented them as nodes. And suppose we wanted to connect all the users on the site, and drew a link between them if they were friends. So if this person's friends with them. If this person's friend made this person's friend and so forth. Just think about how big that graph would be, with billions of nodes and just tons of links connected. So obviously, we can't draw that here and as we'll see there are many companies actually trying to put that graph together for, marketing purposes. But one of the questions are going to come up is what really constitutes a link between Facebook users? So, how we define a link is sometimes a little ambiguous. Because, just two people being friends doesn't necessarily indicate that they interact a lot. Right? Some people are friends on Facebook and they almost never talk. So should it just be a your friendship relationship or should it be some stronger notion like a certain amount of mutual activity on eachother's walls. And these are things that we're going to consider through this lecture. And not far behind Facebook in popularity is Twitter, which we also all know. So a brief timeline of Twitter. It was created in March 2006 by Jack Dorsey, who was an employee at Odeo at the time and it was launched in July of that same year. In April 2007, Twitter officially became and independent company separate from Odeo. And in just six years Twitter attracted more than 500 million users, so, which is about half the number of people who are on Facebook. And on it's seventh anniversary in, March 2013, there were more than 400 million tweets each day that they were handling. So had rose to an average of 400 million tweets, handled each day. So we can identify three features that are integrated on Twitter's platform. First is, having one-way following relationships, which is. Highlights a difference from the likes of Facebook, because on Facebook there has to be a mutual friendship, right? So when you send someone a friend request, they have to accept it before we would draw a link between them. But on Twitter, you can just follow people, and they don't have to make any form of acceptance. So If, this, if this node here is following this note here, then we can just draw a link like that. And, so, th, th this works similar to when we looked at web graphs, in the sense, where you can hyperlink something and they don't necessarily have to hyperlink you back. This is especially true in the case of, like, celebrities. Right? Because you might be a famous celebrity so, I might decide to follow you on Twitter, but that does not by any means. Yeah, indicate that you're going to come and follow me back. So certain people could have many, many more people than that they're following than are being followed by and vice versa. And another feature is microblogging. So Twitter has the idea of which each of these tweets, there's going to be no more than 140 characters. So there's, there's a limit. It's supposed to be short, concise, to the point. You know with hashtags and Facebook I'm sure there's some limit to how much you can write in a single post on Facebook. I'm not sure what that is but it's definitely more than 140 characters. And also, third feature being group texting. So. These three features, particularly the first one of one of my following relationships makes Twitter particularly popular among celebrities. So a lot of pop stars, singers, actors, actresses are going to have they'll have Twitter accounts, and they'll tweet as of making this lecture. The person with the most followers was Katy Perry. And actually as I am writing the network, the network illustrated textbook it had been Justin Bieber and now Justin Bieber is second to Katy Perry. It changes a bit on who is popular, who just had an album, and who has attracted the most followers, and so forth. So, Facebook and Twitter are two of the most influential modes of communication especially among younger generations. Both of them, but Twitter, in particular, tends to spike in usage during major events. So we can look at two interesting examples. In summer 2011, for any of us who live on the East Coast of the US, know that we had a earthquake, which is a very rare occurrence on the East Coast. And tweets traveled faster than the earthquake itself from Virginia to New York. So it, it came in around New York and it eventually got its way over to Virginia. So, what this is, what this graph is showing right here, this is ten seconds and 80 seconds after the earthquake hit and you can see the volume increasing on tweets. So this is, this is volume of tweets that we can see. This is ten seconds after the earthquake hit and this is 80 seconds. So you can see how quickly the amount of tweets just, just skyrocketed even 80 seconds after people just went right to Twitter to announce the fact that there was an earthquake happening. And, another thing two is, in 2013, we can look at the largest events tweeted, we can look those up, you can look those up on the internet. One very unfortunate event, the Boston Marathon bombings. Those had 27.8 million tweets total around that time. So not exactly on the day that it happened, but just in the window of time that it happened, then directly thereafter. At the NBA Finals, there was 26.7 million tweets. And the Super Bowl 2013 all these events being in 2013. There was the Super Bowl attracted 24.1 million tweets. So, clearly during major events people go to Twitter a lot and they also go to Facebook too to give updates or get updates.
