Why test scores should be compared with caution

Expert English language researchers at Georgia State University have compared IELTS Academic and Duolingo English Test (DET). Download the full research report or read our article for a recap.

Duolingo has produced a concordance table between IELTS and DET scores, however the researchers suggest that the relationship between the two tests is not straightforward and the relationship needs to be interpreted with caution. 

Why do we need to be cautious?

Well firstly, the current concordance table is too simplistic a comparison that doesn’t tell us much from a research perspective, and no independent researcher has produced further research to the best of our knowledge.

Secondly, comparisons between scores on different tests is challenging because tests differ in their design, purpose and format (Taylor, 2004, Lim et al, 2013) and the greater the difference in design, the more problematic the comparison is.6

What is important when comparing tests?

The Studies in Test Comparability Series encourages test score users to move beyond a basic comparison of overall scores to a more nuanced awareness of underlying similarities and differences.

“Institutions should consider a range of evidence when setting standards for their specific purposes, as the range of activities sampled by different tests (and the depth in which they do so) differs … the applicability of scores may vary, depending on the range of activities in which applicants will typically be engaged.”7

For test scores to be truly meaningful, we need to broaden our focus beyond simply the language, to focus also on the underlying cognitive demands of the test task. For example, do they reflect the demands of real world language use? We need to understand the social conditions of language use, particularly for speaking.

We also need to compare the scores achieved across the different sections of a test, to draw comparisons around the measurement relationship between the two and answer questions such as how well one test can predict performance on the other.

Further research will be needed in order to meaningfully compare the scores on IELTS Academic and DET.

See the full article

6Taylor, L. (2004). Issues of test comparability, Research Notes 15, 2–5.
Lim, G. S., Geranpayeh, A., Khalifa, H., & Buckendahl, C. W. (2013). Standard setting to an international reference framework: Implications for theory and practice, International Journal of Testing.
7Saville, N., O’Sullivan, B, & Clark. T. (Eds.) (2021). Investigating the relationship between IELTS and PTE-Academic. IELTS Partnership Research Papers: Studies in Test Comparability Series, No. 2. IELTS Partners: British Council, Cambridge Assessment English and IDP: IELTS Australia.