Exploring the effects of task difficulty and learner variables on performance on picture description writing tasks

Picture description (PD) tasks are widely used in second language (L2) teaching, research, and assessment to elicit and/or evaluate L2 learners' writing performance. However, there is little research on the effects of the characteristics of such tasks on L2 writing performance. This study aimed to examine the effects of task difficulty and learner variables on the linguistic characteristics of responses to the 2020 version of the Duolingo English Test (DET) PD writing tasks. The written responses of 1439 test takers from four first language (L1) backgrounds and at different levels of L2 proficiency to 335 DET PD tasks at two levels of difficulty were analyzed and compared in terms of measures of fluency, accuracy, and complexity using various computer programs. The findings indicated that task difficulty did not affect writing performance significantly; high-proficiency learners tended to perform better than did their low-proficiency counterparts; responses receiving higher scores tended to be longer and more accurate; and learner L1 was significantly associated with writing grades and linguistic features. The findings and their implications for the DET PD task and the DET validity argument are discussed.