[Paper Review] Assembling thefacebook: Using heterogeneity to understand online social network assembly

Abigail Z. Jacobs, Samuel F. Way+2 more|arXiv (Cornell University)|Mar 23, 2015

Complex Network Analysis Techniques29 references4 citations

TL;DR

This study investigates the assembly of online social networks using a unique dataset of 100 college networks from Facebook’s early phase (2004–2005). By analyzing temporal dynamics and natural experiments, it reveals a two-phase assembly process—initial sparsification driven by population growth, followed by densification as adoption saturates—highlighting the critical role of offline social context and user heterogeneity in shaping network structure.

ABSTRACT

Online social networks represent a popular and diverse class of social media systems. Despite this variety, each of these systems undergoes a general process of online social network assembly, which represents the complicated and heterogeneous changes that transform newly born systems into mature platforms. However, little is known about this process. For example, how much of a network's assembly is driven by simple growth? How does a network's structure change as it matures? How does network structure vary with adoption rates and user heterogeneity, and do these properties play different roles at different points in the assembly? We investigate these and other questions using a unique dataset of online connections among the roughly one million users at the first 100 colleges admitted to Facebook, captured just 20 months after its launch. We first show that different vintages and adoption rates across this population of networks reveal temporal dynamics of the assembly process, and that assembly is only loosely related to network growth. We then exploit natural experiments embedded in this dataset and complementary data obtained via Internet archaeology to show that different subnetworks matured at different rates toward similar end states. These results shed light on the processes and patterns of online social network assembly, and may facilitate more effective design for online social systems.

Motivation & Objective

• Understand the structural evolution of online social networks during their early growth phase.
• Investigate how network assembly is influenced by user heterogeneity, adoption rates, and temporal dynamics.
• Identify whether distinct developmental phases exist in the maturation of online social networks.
• Explore the impact of offline social context (e.g., on-campus vs. off-campus) on online network formation.
• Use natural experiments in the Facebook100 dataset to isolate causal effects of social proximity and timing on network structure.

Proposed method

• Analyze a longitudinal snapshot of 100 college-based Facebook networks collected in September 2005, with varying vintages and adoption rates.
• Use vintage differences (time since college joined Facebook) to infer temporal dynamics of network assembly.
• Leverage natural experiments based on academic calendar variations (early vs. late start dates) to compare online vs. offline-driven network formation.
• Compare subpopulations (e.g., incoming freshmen, alumni, on-campus vs. off-campus students) to isolate the effects of physical proximity and shared history.
• Apply network metrics such as mean geodesic distance, degree distribution, and assortativity to track structural changes over time.
• Model network evolution as a two-phase process: sparsification (growth with new users and sparse links) followed by densification (increased connections among existing users).

Experimental results

Research questions

• RQ1 How does network structure evolve during the early assembly of online social networks?
• RQ2 To what extent is network assembly driven by simple growth versus structural densification?
• RQ3 How do adoption rates and user heterogeneity (e.g., on-campus vs. off-campus) affect network maturity and topology?
• RQ4 What role does physical proximity and shared offline context play in shaping online social ties?
• RQ5 Are there distinct developmental phases in the assembly of online social networks, and do they vary across subpopulations?

Key findings

• Online social network assembly proceeds through two distinct phases: initial sparsification during population growth, followed by densification as adoption saturates.
• Networks with longer exposure to Facebook—especially on-campus students—exhibited shorter mean geodesic distances, higher average degrees, and less heavy-tailed degree distributions.
• Students who joined Facebook before arriving on campus (off-campus) showed higher opposite-gender assortativity, suggesting online-dating-like behavior due to lack of offline social context.
• In contrast, on-campus students exhibited same-gender assortativity, reflecting the influence of offline social environments on online tie formation.
• The transition from sparsification to densification in the Facebook100 networks aligns with the broader trend observed in the full Facebook network, peaking in mean distance around 2008.
• The study confirms that network structure is not solely a function of growth, but is significantly shaped by social context, timing, and user heterogeneity during early adoption.