This document presents a two-stage approach to predict discussion activity on online community forums. In the first stage, the approach identifies "seed posts" that are likely to generate replies through a classification model using user, content, and topic focus features. The second stage predicts the level of discussion generated by seed posts using regression models. Key findings include that posts with many URLs may reduce activity, while lower forum entropy and more complex language can increase activity. The approach achieved good performance in identifying seed posts and predicting discussion levels. Future work aims to apply the approach to other social media platforms.

1. Anticipating Discussion Activity on Community Forums Matthew Rowe, Sofia Angeletou and HarithAlani Knowledge Media Institute, The Open University, Milton Keynes, United Kingdom The Third IEEE International Conference on Social Computing. MIT, Boston, USA. 2011

2. Community Content 1 Anticipating Discussion Activity on Community Forums Online communities are now used to: Ask questions Post opinions and ideas Discuss events and current issues Content analysis in online communities is attractive for: Market analysis Brand consensus and product opinion Social network analytics in the US is predicted to reach $1 billion by 2014 (Forrester 2009) Masses of data is now being published in online communities: Facebook has more than 60 million status updates per day (Facebook statistics 2010)

3. Anticipating Discussion Activity on Community Forums 2

4. The Need for Analysis Analysts need to know which piece of content will generate the most activity i.e. the most auspicious or influential Helps focus the attention of human and computerised analysts What to track? Need to understand the effect features (community and content) have on attention to content Enable content creators to shape their content in order to maximise impact E.g. promoters, government policy makers RQ1: Which features are key to stimulating discussions? RQ2: How do these features influence discussion length? Anticipating Discussion Activity on Community Forums 3

5. Outline Anticipating Discussion Activity: Approach Overview Identifying Seed Posts Predicting Discussion Activity Features Dataset Community Message Board: Boards.ie 1. Identifying Seed Posts 2. Predicting Discussion Activity Findings Conclusions Anticipating Discussion Activity on Community Forums 4

6. Approach Overview Two-stage approach to predict discussion activity in online communities: 1. Identify seed posts i.e. Thread starters that yield a reply Will a given post start a discussion? What are the properties that seed posts exhibit? What parameters tend to trigger a discussion? 2. Predict discussion activity levels From the identified seed posts What is the level of discussion that a seed post will generate? What features correlate with heightened discussion activity? Anticipating Discussion Activity on Community Forums 5

7. Features For each post, model: a) the author, b) the content and c) the topical concentration of the author F1: User Features In-degree, out-degree: social network properties of the author Post count, age, post rate: participation information of the author F2: Content Features Post length, referral count, time in day: surface features of the post Complexity: cumulative entropy of terms in the post Readability: Gunning Fog index of the post Informativeness: TF-IDF measure of terms within the post Polarity: average sentiment of terms in the post Anticipating Discussion Activity on Community Forums 6

8. Features (2) F3: Focus Features Topic entropy: the concentration of the author across community forums Higher entropy indicates a wider spread of forum activity More random distribution, less concentrated Topic Likelihood: the likelihood that a user posts in a specific forum given his post history Measures the affinity that a user has with a given forum Lower likelihood indicates a user posting on an unfamiliar topic Anticipating Discussion Activity on Community Forums 7

9. Dataset: Boards.ie Irish community message board that was established in 1998 Covers a wide array of topics and themes in forums E.g. World of Warcraft, Japanese Culture, Rugby We were provided with the complete dataset spanning 1998-2008 of all posts and forum information Focussed on 2006 due to the scale of entire dataset No explicit social connections exist in the dataset Social network features were built from the reply-to graph 6-month window prior to the post date was used to build the user and focus features Anticipating Discussion Activity on Community Forums 8

10. 1. Identifying Seed Posts Will a given post start a discussion? What are the properties that seed posts exhibit? Experiment Setup: Used all thread starter posts from Boards.ie in 2006 Training/validation/testing sets using a 70/20/10% random split Binary classification task: Is this a seed post or not? Measures: precision, recall, f-measure, area under ROC curve Performed 2 experiments: a) Model Selection Tested individual feature sets (user, content, focus) and combinations b) Feature Assessment Dropping 1 feature at a time, record reduction in f-measure Anticipating Discussion Activity on Community Forums 9

11. 1.a) Model Selection Anticipating Discussion Activity on Community Forums 10

12. 1.b) Feature Assessment Anticipating Discussion Activity on Community Forums 11

13. 1.b) Feature Assessment Anticipating Discussion Activity on Community Forums 12

14. 2. Predicting Discussion Activity What is the level of discussion that a seed post will generate? What features correlate with heightened discussion activity? Experiment Setup: Train: seed posts in 70% training split Test: seed posts in 20% validation split Measure: Normalised Discounted Cumulative Gain (nDCG) Look at varying rank positions: nDCG@k, k=1,2,5,10,20,50,100 Performed 2 experiments a) Model Selection Regression models: Linear, Isotonic, Support Vector Regression Tested individual feature sets (user, content, focus) and combinations b) Feature Contributions Assess the features in the best performing model from a) Anticipating Discussion Activity on Community Forums 13

15. 2.a) Model Selection Anticipating Discussion Activity on Community Forums 14

16. 2.a) Model Selection Anticipating Discussion Activity on Community Forums 15 Support Vector Regression Isotonic Linear

17. 2.b) Feature Contributions What features correlate with heightened discussion activity? Anticipating Discussion Activity on Community Forums 16

19. Negative sentiment posts generate more activityAnticipating Discussion Activity on Community Forums 17

20. Conclusions and Future Work The two-stage approach is able to: Identify seed posts to a high degree of accuracy F-measure: 0.792 Predict discussion activity levels nDCG@1: 0.89 (linear regression model) Content and focus features yield best performing model Average nDCG@k: 0.756 Findings inform: Market Analysts to track high activity posts from the outset Content creators to shape content in order to maximise impact Currently applying approach over different platforms: How can we predict activity on a given social web system? How do social web systems differ in generate activity? Anticipating Discussion Activity on Community Forums 18

21. Anticipating Discussion Activity on Community Forums 19 Questions? Web: http://people.kmi.open.ac.uk/rowe Email: m.c.rowe@open.ac.uk Twitter: @mattroweshow