Assessing syntactic and lexicogrammatical use in second language Mandarin writing samples

General indices of syntactic complexity (e.g. mean length of T-unit, clauses per T-Unit) have long been used to measure the writing proficiency of adult language learners (Bulté & Housen, 2012; Norris & Ortega, 2006; Ortega, 2003; Wolfe-Quintero et al., 1998). In contrast, a number of recent studies have focused on measuring adult second language writing proficiency using methods rooted in usage-based theories of language learning. The present study extends previous research (e.g., Kyle & Crossley, 2017) by comparing usage-based and general indices of syntactic and lexicogrammatical use in learners of Mandarin. It also extends previous work by investigating whether meaningful, but non-linear trends exist. To do this, it first compares multiple linear regression models to polynomial models for general and usage-based indices respectively. Then it compares the strongest model for each type of index to determine which is better. Consistent with Kyle and Crossley (2017), it finds that in Mandarin usage-based indices are better predictors of proficiency than general indices and that the frequency of the verb decreases over time while the strength of association between verb and VAC increases. Furthermore, non-linear trajectories were found to exist in general indices while usage-based indices were linear.