Does Welsh media need a review? Detecting bias in Nation.Cymru's political reporting

TL;DR

This study uses NLP techniques to detect bias in Welsh media, revealing differential framing of political parties and providing a framework for broader media bias analysis.

Contribution

It introduces a two-stage NLP pipeline combining bias detection and sentiment classification to analyze media bias in Welsh political reporting.

Findings

Reform UK is biased twice as often as Plaid Cymru.

Plaid Cymru receives more favorable framing than other parties.

The pipeline is low-cost and replicable for broader media bias studies.

Abstract

Wales' political landscape has been marked by growing accusations of bias in Welsh media. This paper takes the first computational step toward testing those claims by examining Nation.Cymru, a prominent Welsh political news outlet. I use a two-stage natural language processing (NLP) pipeline: (1) a robustly optimized BERT approach (RoBERTa) bias detector for efficient bias discovery and (2) a large language model (LLM) for target-attributed sentiment classification of bias labels from (1). A primary analysis of 15,583 party mentions across 2022-2026 news articles finds that Reform UK attracts biased framing at twice the rate of Plaid Cymru and over three times as negative in mean sentiment (p<0.001). A secondary analysis across four parties across both news and opinion articles shows that Plaid Cymru is the outlier, receiving markedly more favourable framing than any other party. These findings provide evidence of measurable differential framing in a single Welsh political media outlet, supporting calls for a broader review of Welsh media coverage. Furthermore, the two-stage pipeline offers a low-cost, replicable framework for extending this analysis to other Welsh outlets, as well as media ecosystems outside of Wales.