422 citations · 1.7k across the 22 of their papers we have counts for
23 papers
When 'For You' Isn't For You: Measuring User Agency in TikTok's Algorithmic Feed
Levi Kaplan, Devin Patel, Nicole Gerzon +2
The short-form video-sharing service TikTok has become an important platform in the social media landscape, with much of its popularity owed to its algorithmically-driven "For You…
On the Use of Proxies in Political Ad Targeting
Piotr Sapiezynski, Levi Kaplan, Alan Mislove +1
Detailed targeting of advertisements has long been one of the core offerings of online platforms. Unfortunately, malicious advertisers have frequently abused such targeting feature…
Problematic Advertising and its Disparate Exposure on Facebook
Muhammad Ali, Angelica Goetzen, Alan Mislove +2
Targeted advertising remains an important part of the free web browsing experience, where advertisers' targeting and personalization algorithms together find the most relevant audi…
Evolution of Digital Advertising Strategies during the 2020 US Presidential Primary
NaLette Brodnax, Piotr Sapiezynski
Political advertising on digital platforms has grown dramatically in recent years as campaigns embrace new ways of targeting supporters and potential voters. Previous scholarship s…
The switching mechanisms of social network densification
Teruyoshi Kobayashi, Mathieu Génois
Densification and sparsification of temporal networks are attributed to two fundamental mechanisms: a change in the population in the system and/or a change in the chances that nod…
The Fallibility of Contact-Tracing Apps
Piotr Sapiezynski, Johanna Pruessing, Vedran Sekara
Since the onset of the COVID-19's global spread we have been following the debate around contact tracing apps -- the tech-enabled response to the pandemic. As corporations, academi…
Ad Delivery Algorithms: The Hidden Arbiters of Political Messaging
Muhammad Ali, Piotr Sapiezynski, Aleksandra Korolova +2
Political campaigns are increasingly turning to digital advertising to reach voters. These platforms empower advertisers to target messages to platform users with great precision,…
Algorithms that "Don't See Color": Comparing Biases in Lookalike and Special Ad Audiences
Piotr Sapiezynski, Avijit Ghosh, Levi Kaplan +2
Researchers and journalists have repeatedly shown that algorithms commonly used in domains such as credit, employment, healthcare, or criminal justice can have discriminatory effec…
Discrimination through optimization: How Facebook's ad delivery can lead to skewed outcomes
Muhammad Ali, Piotr Sapiezynski, Miranda Bogen +3
The enormous financial success of online advertising platforms is partially due to the precise targeting features they offer. Although researchers and journalists have found many w…
Quantifying the Impact of User Attention on Fair Group Representation in Ranked Lists
Piotr Sapiezynski, Wesley Zeng, Ronald E. Robertson +2
In this work, we introduce a novel metric for auditing group fairness in ranked lists. Our approach offers two benefits compared to the state of the art. First, we offer a blueprin…
Offline Behaviors of Online Friends
Piotr Sapiezynski, Arkadiusz Stopczynski, David Kofoed Wind +2
In this work we analyze traces of mobility and co-location among a group of nearly 1000 closely interacting individuals. We attempt to reconstruct the Facebook friendship graph, Fa…
Detrimental Network Effects in Privacy: A Graph-theoretic Model for Node-based Intrusions
Florimond Houssiau, Piotr Sapiezynski, Laura Radaelli +2
Despite proportionality being one of the tenets of data protection laws, we currently lack a robust analytical framework to evaluate the reach of modern data collections and the ne…
The Role of Gender in Social Network Organization
Ioanna Psylla, Piotr Sapiezynski, Enys Mones +1
The digital traces we leave behind when engaging with the modern world offer an interesting lens through which we study behavioral patterns as expression of gender. Although gender…
Measuring Personalization of Web Search
Anikó Hannák, Piotr Sapieżyński, Arash Molavi Khaki +3
Web search is an integral part of our daily lives. Recently, there has been a trend of personalization in Web search, where different users receive different results for the same s…
Academic Performance and Behavioral Patterns
Valentin Kassarnig, Enys Mones, Andreas Bjerre-Nielsen +3
Identifying the factors that influence academic performance is an essential part of educational research. Previous studies have documented the importance of personality traits, cla…
Evidence of Complex Contagion of Information in Social Media: An Experiment Using Twitter Bots
Bjarke Mønsted, Piotr Sapieżyński, Emilio Ferrara +1
It has recently become possible to study the dynamics of information diffusion in techno-social systems at scale, due to the emergence of online platforms, such as Twitter, with mi…
Inferring Person-to-person Proximity Using WiFi Signals
Piotr Sapiezynski, Arkadiusz Stopczynski, David Kofoed Wind +2
Today's societies are enveloped in an ever-growing telecommunication infrastructure. This infrastructure offers important opportunities for sensing and recording a multitude of hum…
Multi-scale spatio-temporal analysis of human mobility
Laura Alessandretti, Piotr Sapiezynski, Sune Lehmann +1
The recent availability of digital traces generated by phone calls and online logins has significantly increased the scientific understanding of human mobility. Until now, however,…
Evidence for a Conserved Quantity in Human Mobility
Laura Alessandretti, Piotr Sapiezynski, Vedran Sekara +2
Recent seminal works on human mobility have shown that individuals constantly exploit a small set of repeatedly visited locations. A concurrent literature has emphasized the explor…
Temporal Fidelity in Dynamic Social Networks
Arkadiusz Stopczynski, Piotr Sapiezynski, Alex 'Sandy' Pentland +1
It has recently become possible to record detailed social interactions in large social systems with high resolution. As we study these datasets, human social interactions display p…
Tracking Human Mobility using WiFi signals
Piotr Sapiezynski, Arkadiusz Stopczynski, Radu Gatej +1
We study six months of human mobility data, including WiFi and GPS traces recorded with high temporal resolution, and find that time series of WiFi scans contain a strong latent lo…
Measuring large-scale social networks with high resolution
Arkadiusz Stopczynski, Vedran Sekara, Piotr Sapiezynski +4
This paper describes the deployment of a large-scale study designed to measure human interactions across a variety of communication channels, with high temporal resolution and span…
Crowds, Bluetooth, and Rock-n-Roll. Understanding Music Festival Participant Behavior
Jakob Eg Larsen, Piotr Sapiezynski, Arkadiusz Stopczynski +2
In this paper we present a study of sensing and analyzing an offline social network of participants at a large-scale music festival (8 days, 130,000+ participants). We place 33 fix…