This paper explores the sociolinguistic predictors of Mandarin-English codeswitching, and also tests such patterns against current syntactic constraints of codeswitching. By doing so, I demonstrate the value of incorporating sociolinguistic factors as predictors into computational models of codeswitching, explored in a companion paper (Yi 2022). The study presented here draws from novel data collected from 12 Mandarin-English bilingual speakers from Grand Rapids, Michigan. These speakers come from two generations, correlated with their age and immigration history. Speakers participated in sociolinguistic interviews that were designed to elicit codeswitching in narrative-style responses on a variety of topics, including family, school, and culture. Participants also answered metalinguistic questions about their own language practices and attitudes and completed a written Language History Questionnaire (LHQ) (Li et al. 2020), which asked for self-evaluations of language habits (proficiency, immersion, and dominance in the two languages). LHQ responses were then quantified into “scores” that served as sociolinguistic predictors for the companion paper (Yi 2022). Patterns found in this novel Mandarin-English data frequently, and potentially systematically, violate many of the currently proposed syntactic constraints on codeswitching (which mainly come from research on Spanish-English bilinguals), implying that the constraints may not be universal, and that new avenues should be considered for understanding the morphosyntax of bilingual codeswitching.