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Article published In: Advanced Quantitative Methods in Bi-/Multilingualism
Edited by Christos Pliatsikas, George Pontikas and Ian Cunnings
[Linguistic Approaches to Bilingualism 15:4] 2025
► pp. 487–517

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Optimising participant grouping methods in bilingualism studies

Insights from eye-tracking data

ORCiD logo with link | University of Birmingham
ORCiD logo with link | University of Birmingham
ORCiD logo with link | University of Birmingham
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Available under the Creative Commons Attribution (CC BY) 4.0 license.

For any use beyond this license, please contact the publisher at rights@benjamins.nl.

Open Access publication of this article was funded through a Transformative Agreement with University of Birmingham.

Published online: 28 April 2025
DOI logo with link
https://doi.org/10.1075/lab.24019.he
Abstract
This research addresses two major challenges in studying second language acquisition and bilingualism: reducing overlap in predictor variables and correctly classifying participants into language proficiency levels. Too many relevant predictors can harm statistical analysis due to an increased chance of overlap, known as multicollinearity. To tackle this, we use Principal Component Analysis (PCA) on selected predictors to identify proficiency indicators, combining the length of stay in the UK and language test scores. Additionally, traditional methods, especially IELTS-based proficiency classifications, often miss subtle differences in language skills, particularly when they fail to consider how long participants have been exposed to the target language. We counter this by using non-hierarchical Cluster Analysis (NCA) for a grounded, data-driven way of detecting distinct language proficiency groups. This new approach is demonstrated on a dataset of eye movements from reading tasks, collected from Chinese–English bilinguals in the UK.
Article outline
  • 1.Introduction
    • 1.1Critical predictors in bilingual reading and the problem of multicollinearity
    • 1.2L2 reading models and developmental trajectories
    • 1.3Participant grouping methods in bilingualism research
    • 1.4This study
  • 2.Methods
    • 2.1Participants
    • 2.2Language history questionnaires and vocabulary test
    • 2.3Reading stimuli
    • 2.4Apparatus
    • 2.5Procedure
    • 2.6Eye-Movement Variables
    • 2.7Data preparation
      • Random factors
      • Controls
      • Covariates
  • 3.Data analysis and results
    • 3.1Clustering Chinese participants
      • Correlation analysis
      • Principal component analysis
    • 3.2Statistical modelling of first fixation durations
  • 4.Discussion
  • 5.Conclusions
  • Acknowledgements
  • Declaration of competing interest
  • Data availability statement
  • Notes
  • References
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Pliatsikas, Christos, George Pontikas & Ian Cunnings
2025. Applying advanced quantitative methods in bi-/multilingualism. Linguistic Approaches to Bilingualism 15:4 ► pp. 425 ff. DOI logo

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