This paper investigates how boosters are used by qualitative and quantitative research article writers to express certainty. Boosters are words such as "definitely," "sure," "demonstrate" which signal writers' assurance in what they say. Drawing on a corpus of 200 research articles in Applied Linguistics, this study compares the use of boosting words in the Discussion sections of qualitative and quantitative research articles in Applied Linguistics. The focus is on the frequency, main functions and form of boosters in these two sets of articles.