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Diverging patterns of interaction around news on social media: insularity and partisanship during the 2018 Italian election campaign

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Giglietto, F., Valeriani, A., Righetti, N., & Marino, G. (2019). Diverging patterns of interaction around news on social media: insularity and partisanship during the 2018 Italian election campaign. Information, Communication & Society. https://doi.org/10.1080/1369118X.2019.1629692

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Summary

This paper investigates how partisan communities engaged with political news on social media during Italy’s 2018 general election. Combining Twitter data to classify news sources by partisan attention and Facebook engagement metrics on 84,815 political news stories, the authors introduce an “insularity” measure and examine how it shapes patterns of sharing versus commenting. They find that sources favored by supporters of populist parties (Five Star Movement/M5S and the League) are more insular; insular sources are amplified through shares while cross-partisan sources become sites of comment-based contestation; and M5S uniquely benefits from a strategic pattern where positive stories are amplified and negative stories contested. The authors argue that populist success rests on both ideological affinity with fragmented hybrid media and long-term investment in digital infrastructure, exemplified by M5S as an “anti-elitist cyber party.”

Key Contributions

  • Extends Faris et al.’s Media Partisanship Attention Score (MPAS) into a Multi-Party MPAS (MP-MPAS) applicable to multiparty systems beyond the US two-party context.
  • Introduces a novel source-level “insularity” index combining maximum partisan attention with a Gini coefficient of partisan dispersion.
  • Triangulates Twitter (for partisan attention estimation) with Facebook (for engagement patterns), offering a methodological template that navigates platform data-access constraints.
  • Provides empirical evidence from a polarized-pluralist multiparty system, complementing the mostly US-based literature.
  • Nuances the echo-chamber thesis by showing cross-partisan sources are loci of contestation, not merely absent from partisan diets.
  • Advances a “cyber party” argument linking populism with strategic exploitation of social media attention economies.

Methods

The authors collected ~216,765 retweets of Italian party/leader accounts in January 2018 to estimate user partisanship, then tracked the top 5,000 partisan contributors’ tweets (~4.4M tweets, ~130M resolved URLs) via DMI-TCAT to compute MP-MPAS scores for 634 news sources. Insularity was operationalized as a combination of a source’s maximum MP-MPAS and the Gini coefficient of its score distribution, yielding four tiers. Facebook engagement data on 84,815 stories from 4,113 domains (Sept 2017–March 2018) were gathered via the Graph API. Manual sentiment coding was performed on the top-decile (3,731) most-engaged stories by three coders (Krippendorff’s α = 0.72–0.84). Analyses used Kruskal-Wallis, Dunn’s post-hoc with Bonferroni correction, and Spearman correlations.

Findings

  • Median insularity: M5S sources = 0.73, League = 0.67, LeU = 0.63, PD = 0.63 (system mean 0.65); M5S significantly higher than all others (p < .001).
  • Attribution of 634 sources: League 33.9%, M5S 27.9%, cross-partisan 19.1%, PD 9.5%, LeU 7.7%; Forza Italia and FdI attracted almost no adjudicated sources.
  • Insularity is negatively correlated with the comments/shares ratio (Spearman ρ = -.31, p < .001): insular sources are amplified via shares; cross-partisan sources attract commenting.
  • M5S: positive stories → more shares per comment; negative stories → more comments per share (p < .001).
  • PD, Forza Italia, League: the opposite pattern — negative stories were amplified, positive stories contested.
  • Cross-partisan, low-insularity sources functioned as arenas of contestation rather than echo-chamber amplification.

Connections

This paper is part of a sustained research program by the same team on the Italian information ecosystem, connecting closely to Giglietto2020-9d8acdd7, Giglietto2022-0e951ac5, Giglietto2023-fa71a001, Giglietto2025-1765bb4f, Giglietto2025-1e9a0917, and Marino2023-9137f448, which extend the study of partisan coordination, problematic information, and cross-platform dynamics in Italy. It also speaks to broader debates on populist mobilization and hybrid media addressed in Mosca2026-yh and Ducci2022-10cb5d70, and to cross-national work on partisan attention and echo chambers such as Gonzalez-Bailon2024-rq.

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