Language inclusion in ecological systematic reviews and maps: Barriers and perspectives

Hannah, K., Haddaway, N.R., Fuller, R.A. & Amano, T. (2024) Research Synthesis Methods.

Systematic reviews and maps are considered a reliable form of research evidence, but often neglect non-English-language literature, which can be a source of important evidence. To understand the barriers that might limit authors’ ability or intent to find and include non-English-language literature, this paper assessed systematic reviews and maps published in Environmental Evidence (n = 72) and also surveyed authors from each paper (n = 32 responses).

The paper found that 44% of the reviewed papers (32/72) excluded non-English literature from their searches and inclusions. Commonly cited reasons included constraints related to resources (especially relevant language skills) and time (Figure 1). Regression analysis revealed that reviews with larger author teams, authors from diverse countries, especially those with non-English primary languages, and teams with multilingual capabilities searched in a significantly greater number of non-English languages (Figure 2). The survey exposed limited language diversity within the review teams and inadequate funding as the principal barriers to incorporating non-English language literature.

To improve language inclusion and reduce bias in systematic reviews and maps, our study suggests increasing language diversity within review teams. Combining machine translation with language skills can alleviate the financial and resource burdens of translation. Funding applications could also include translation costs. Additionally, establishing language exchange systems would enable access to information in more languages. Further studies investigating language inclusion in other journals would strengthen these conclusions.

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Figure 1. Count of barriers that impeded the searching for and screening of non-English-language articles in the specific systematic review/map published in Environmental Evidence. The 32 respondents were allowed to select multiple barriers.

Figure 2. Relationships between the number of languages searched in each systematic review/map and (a) the percentage of authors associated with countries where English is a primary language and (b) the number of author countries. The regression lines are based on the fitted Poisson generalised linear model with 95% confidence intervals shown as shaded areas and with the exclusion of an outlying datapoint. Jitter is used to show all data points.