Community-based question answering (CQA) platforms are crowd-sourced services for sharing user expertise on various topics, from mechanical repairs to parenting. While they naturally build-in an online social network infrastructure, they carry a very different purpose from Facebook-like social networks, where users “hang-out” with their friends and tend to share more personal information. It is unclear, thus, how the privacy concerns and their correlation with user behavior in an online social network translate into a CQA platform. This study analyzes one year of recorded traces from a mature CQA platform to understand the association between users’ privacy concerns as manifested by their account settings and their activity in the platform. The results show that privacy preference is correlated with behavior in the community in terms of engagement, retention, accomplishments and deviance from the norm. We find privacy-concerned users have higher qualitative and quantitative contributions, show higher retention, report more abuses, have higher perception on answer quality and have larger social circles. However, at the same time, these users also exhibit more deviant behavior than the users with public profiles. I. Kayes, N. Kourtellis, D. Quercia, A. Iamnitchi and F. Bonchi. Privacy Concerns vs. User Behavior in Community Question Answering. In IEEE/ACM ASONAM, Aug. 2015.

1. 7th IEEE/ACM International Conference on Advances in Social Networks Analysis and Mining
Privacy Concerns vs. User Behavior
in Community Question Answering
Imrul Kayes
USF
Nicolas Kourtellis
Telefonica Research
Francesco Bonchi
Yahoo Labs
Adriana Iamnitchi
USF

2. 7th IEEE/ACM International Conference on Advances in Social Networks Analysis and Mining
Community Question Answering Sites
• CQA sites: Popular platforms
– Yahoo Answers: 200M users, 5M users/day
– Quora: 1M/month
– Stack Exchange: 4M users (e.g., Stack Overflow)
• Functionalities:
– Q/A posts & comments, social networking,
leaderboards, and more.
• Why do we need them?
– Not all web-searches are successful!
– Complicated / intricate questions!
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3. 7th IEEE/ACM International Conference on Advances in Social Networks Analysis and Mining
Motivation
• Privacy of user data: important but unresolved issue
• Privacy vs. platform usability:
– Public content is helpful but users would prefer privacy
• Privacy-aware users are more engaged (e.g., on FB)
– Is there a sweet-spot?
2
Privacy
Platform usability

4. 7th IEEE/ACM International Conference on Advances in Social Networks Analysis and Mining
Main Idea
• Utilize users’ modifications on privacy settings
as a proxy of privacy concerns
• Group users into privacy categories:
1. Public
2. Semi-private
• QA-private, Network-private
3. Private
• Study users’ engagement vs. privacy concerns
– Use activity logs & privacy settings instead of
surveys
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5. 7th IEEE/ACM International Conference on Advances in Social Networks Analysis and Mining
Outline
• CQA platforms
• Motivation
• Main idea
• Research Questions
• Yahoo Answers Dataset
• Results
• Proposals for CQA platforms improvements
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6. 7th IEEE/ACM International Conference on Advances in Social Networks Analysis and Mining
Motivating Research Questions
1. Are privacy-concerned users more engaged than
public users?
– Retention, social circles
2. Do privacy-concerned users contribute
differently to the community than public users
– Points, best answers
3. Do privacy-concerned users have different
perception on answer quality than public users?
– Thumbs up/down of best answers
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7. 7th IEEE/ACM International Conference on Advances in Social Networks Analysis and Mining
Motivating Research Questions
4. Are privacy-concerned users also more abuse-
conscious?
– Abuse reporting
5. Are privacy-concerned users more likely to
violate community rules?
– Deviance score
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8. 7th IEEE/ACM International Conference on Advances in Social Networks Analysis and Mining
Yahoo Answers Dataset
• 1.5M users (2012-2013)
– 2.6M follower-followee ties (SN properties*)
– LCC: 1.1M nodes (74%), 2.4M edges (92%)
• Keep active users with more than 10 Q/A (68%)
• 4 privacy settings:
– All public (84.4%), PU
– Hide content (Questions/Answers) (2.5%), QA
– Hide network (Followers/Followees) (0.9%), N
– Hide content & network (12.2%), PR
7
Public
Semi-
Private
Private
*Kayes et al. “The social world of content abusers in Community Question
Answering“, WWW’2015

9. 7th IEEE/ACM International Conference on Advances in Social Networks Analysis and Mining
Privacy & Retention
• Semi-private users have higher inter-event time
• Private users have lower inter-event time
T =
8
T j = (tk+1 -tk )
kÎFj
Fj
Õ
é
ë
ê
ê
ù
û
ú
ú
1/ Fj
, where Fj = {fair events of user j}
Compute T j,"jÎ P, " P Î {PU, QA, N, PR} Retentionj = 1
T j

10. 7th IEEE/ACM International Conference on Advances in Social Networks Analysis and Mining
Privacy & Social Circles
Indegree = #followers, Outdegree = #followees
• Privacy-concerned users have larger social circles
• Followers or followees
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11. 7th IEEE/ACM International Conference on Advances in Social Networks Analysis and Mining
Privacy & Accomplishments
• Private & semi-private users have more points
• Privacy-concerned users contribute more in YA
quantitatively
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12. 7th IEEE/ACM International Conference on Advances in Social Networks Analysis and Mining
Privacy & Accomplishments
best answer percentage (BAP
• Privacy-concerned users contribute more in YA
qualitatively
11

13. 7th IEEE/ACM International Conference on Advances in Social Networks Analysis and Mining
Privacy & Best Answers
• Privacy-concerned users select more Best Answers
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14. 7th IEEE/ACM International Conference on Advances in Social Networks Analysis and Mining
• Community feedback via thumbs up and down:
• Privacy-concerned users have more average thumbs on
Best Answers
Privacy & Best Answer Quality
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15. 7th IEEE/ACM International Conference on Advances in Social Networks Analysis and Mining
Privacy & Abuse Reporting
• 90% of reports submitted by 8% of users
• Privacy-concerned users post more valid reports
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16. 7th IEEE/ACM International Conference on Advances in Social Networks Analysis and Mining
Privacy & Deviance
• Deviance can indicate user engagement*
• Private > semi-private > public users’ deviance scores
15
* Kayes et al. “The social world of content abusers in community
question answering“, WWW’2015

17. 7th IEEE/ACM International Conference on Advances in Social Networks Analysis and Mining
Summary
1. 87.20% public profiles (default)
2. Privacy-concerned users are more engaged:
– higher retention
– more social network contacts
– contribute more & better content
– higher perception on answer quality
– better citizens in terms of reporting abuses
– higher platform engagement (via deviance)
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18. 7th IEEE/ACM International Conference on Advances in Social Networks Analysis and Mining
Suggestions for better CQA platforms
• If privacy settings modified:
– Likely commitment to the platform
– Question recommendation and routing
– Community moderation
• If privacy settings unmodified:
– Incentivize for increased participation & retention
• Privacy settings in CQA sites
– Prediction & recommendation via ML techniques
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19. 7th IEEE/ACM International Conference on Advances in Social Networks Analysis and Mining
Privacy Concerns vs. User Behavior
in Community Question Answering
Imrul Kayes
USF
Nicolas Kourtellis
Telefonica Research
Francesco Bonchi
Yahoo Labs
Adriana Iamnitchi
USF
Paper: http://arxiv.org/abs/1508.06184
nicolas.kourtellis@telefonica.com
Twitter: @kourtellis