Diachronic change of noun phrase complexity in the IMRD sections of medical research articles (1970–2020)

Despite the growing interest in noun phrase (NP) complexity in academic writing, it remains unknown how NP complexity has evolved in IMRD (Introduction, Methods, Results, Discussion) sections within research articles (RAs). Exploring the evolution of NP complexity across sections can not only complement previous diachronic findings on whole RAs, but also enhance our dynamic understanding of the evolving linguistic correlates of IMRD sections with distinct communicative functions. This study investigated the diachronic changes in the use of nine NP complexity features (i.e., noun modifiers) across IMRD sections in a corpus of 480 medical RAs spanning 50 years (1970–2020) at 10-year intervals. Using Pearson correlation tests and two-way ANOVAs, we tracked the changing patterns of each feature and compared those patterns across IMRD sections. Findings showed an upward trend in phrasal NP complexity features in all the sections. Additionally, the cross-sectional comparisons revealed a two-way distinction, in which Introduction/Discussion sections consistently applied a wider range and a larger number of NP complexity features than Methods/Results sections. The observed diachronic changes were explained in relation to the evolving characteristics of the IMRD sections through a text-linguistic analysis. This study may provide useful implications for English for Medical Purposes pedagogy.