1. Mojtaba Torkjazi, Reza Rejaie, Walter Willinger University of Oregon AT&T Labs-Research WOSN09 Barcelona, Spain

2. Motivation A majority of empirical studies of Online Social Networks (OSNs) has focused on their associated friendship graphs What about the temporal dynamics of OSNs? What about the active portion of an OSN? A majority of empirical studies of OSNs has examined the growth of these systems What about the patterns of decline in user population? What about changes over time in user activity? A majority of empirical studies of OSNs has been based on connectivity information What about timing information? How to obtain relevant timing information? 8/17/2009WOSN 2009 - Barcelona2

3. Related Work Characterization of popular OSNs via their friendship graphs OSN characterization in terms of well-known graph metrics [Mislove et al.07, Ahn et al.07, …] Examining the evolution of friendship graphs of popular OSNs OSN evolution in terms of growth metrics and models [Kumar et al.06, Leskovec et al,06, Leskovec et al.08, …] Beyond friendship graphs: Activity graphs Static case (Cyworld) [Chun et al.08] Its all about dynamics! [Willinger et al.09] User interactions in Facebook [Viswanath et al.09 – WOSN09] User interactions in Flickr [Valafar et al.09 – WOSN09] 8/17/2009WOSN 2009 - Barcelona3

4. This Study We examine the evolution of user population and user activity in MySpace User arrival/activity/departure, life cycle of MySpace Why MySpace? It is one of the largest and most popular OSNs It provides several features making our study feasible Main challenges OSNs are often studied when they are popular and the number of departure is negligible Popular OSNs tend to hide the information about user departures 8/17/2009WOSN 2009 - Barcelona4

5. MySpace Features (I) Provides explicit profile status Public Private Invalid Availability of users last login Enables assessment of the level of activity among users Importantly, allows inference of population growth of MySpace (see later for details) Global visibility http://www.myspace.com/user_id 8/17/2009WOSN 2009 - Barcelona5

6. MySpace Features (II) Monotonic assignment of numeric ID Searched periodically for currently smallest unassigned ID and checked that all larger IDs are unassigned; after waiting for a short period, we observed that the smallest unassigned ID (and others after it) are now assigned. Found no apparent patterns in gaps between consecutive invalid IDs No evidence for re-assignement of deleted IDs Makes the selection of random samples of MySpace users easy. 8/17/2009WOSN 2009 - Barcelona6 No visible pattern

7. Measurement Feb. 26 th 2009: MySpace ID space [1 … 455,881,700] 50 parallel samplers to collect 360K users in less than 12 hours (0.1% of MySpace population) Using HTML parser to post-process the downloaded profiles and extract User s profile status (invalid, public, private) Users last login date Users friend list (only for public profiles) Unable to parse last login info for 0.96% of public and 0.08% of private profiles Last login info is not provided or is provided with obvious errors (e.g. 1/1/0001) 8/17/2009WOSN 2009 - Barcelona7

8. On the Population size of MySpace Population of valid MySpace users (Feb. 26, 2009) was about (41.5 + 17.3)% of 455,881,700 = 268M Compare with www.myspace.com/tom who has 266,029,430 friends (Aug. 13, 2009)www.myspace.com/tom How has MySpace grown during the past years? How many active users are there in MySpace? 8/17/2009WOSN 2009 - Barcelona8 TotalInvalidPublicPrivate 362K149K (41.2%)150K (41.5%)63K (17.3%)

9. On User Arrival 8/17/2009WOSN 2009 - Barcelona9 Public users What does u ser ID say about account creation time? Plot user ID vs. last login of that user for all our users Private users

10. On User Arrival 32% of public and 18% of private users are tourists Discovery of tourists enables accurate estimation of user account creation time based on their associated user ID 8/17/2009WOSN 2009 - Barcelona10 Tourists What does user ID say about account creation time? Clean edge = users whose last login is shortly after their account creation time = MySpace tourists

11. On MySpaces Growth Use the observed uniform spread of tourists across entire ID space Estimate account creation time by last login time Estimate account creation time of all sampled accounts based on their ID. 8/17/2009WOSN 2009 - Barcelona11 April 2008 Estimating the user population of MySpace in the past ? Slope of the top line shows the growth rate of MySpace population Exponential growth until about April 2008 Visible knee around April 2008 followed by a slow-down in growth

12. On User Activity (I) Active = login into MySpace within the last 10 days More than half of public users haven't logged into MySpace in the last 100 days Less than one third of private users have logged into MySpace in the last 10 days 8/17/2009WOSN 2009 - Barcelona12 How many active users are there in MySpace? MySpace has about (15% * 41.4% + 35% * 17.3%) * 445,881,700 = 55M active users.

13. On User Activity (II) More active public users in the first half of the ID space More inactive private users in the first half of ID space More med active private & public users in 2nd half of ID space 8/17/2009WOSN 2009 - Barcelona13 Public users Age of a user in the system vs. level of activity? Private users

14. On User Activity (III) No strong correlations in general Except for the very inactive users who tend to have very inactive friends 8/17/2009WOSN 2009 - Barcelona14 Activity of a user vs. activity of the users friends? Public users

15. On User Departure 8/17/2009WOSN 2009 - Barcelona15 More public and private profiles in the first half of ID space More invalid profiles in the second half of ID space Users joining the system earlier have been more likely to keep their accounts than newer users Are newer users more likely to leave than older ones?

16. MySpace Life Cycle (I) Slow-down in the growth rate of MySpace is related to emergence of Facebook Informal evidence (Alexa.com): Daily accesses to Facebook surpassed that of MySpace, at around April 2008 8/17/2009WOSN 2009 - Barcelona16 Possible reasons behind MySpaces decline?

17. MySpace Life Cycle (II) Scalability System design cant cope with exponential growth rates? How to effectively link millions of like-minded users? Security The larger the more attractive to hackers and spammers? More privacy violations and unwanted traffic? Innovation In the absence of constant innovation, initial excitement of users fades away? 8/17/2009WOSN 2009 - Barcelona17 Possible causes for users migrating from one OSN to another ? Is it the case that OSNs become the victim of their own popularity and success?

18. Conclusions We examine the evolution of user population and user activity in MySpace and we found that Estimated population of MySpace users with valid accounts is about 268M, of which only about 55M are active users (as of February 26, 2009). 32% of valid public and 18% of valid private profiles belong to tourists = users with last login shortly after account creation We exploit the existence of these tourists to estimate the population growth of MySpace since its beginning We observe an exponential initial growth rate for MySpace followed by sudden slow-down around April 2008. We speculate about possible reasons for why some OSNs are able to compete and strive in the Internet's OSN eco- system, while others decline and die out. 8/17/2009WOSN 2009 - Barcelona18

19. Future Work What about other OSNs? Twitter, Flickr, YouTube vs. Facebook Measurement challenges Obtaining more/any timing information for user activity Tracking migrating OSN users What factors are key for the success /failure of OSNs Technological, socio-economical, …

20. Thank You Questions? Website http://mirage.cs.uoregon.edu/OSN Contact for code and data: Mojtaba Torkjazi moji@cs.oregon.edu