A variety of linguistic, processing, and social factors have been shown to be associated with concord in existential there constructions (e. g., Meechan and Foley 1994; Tagliamonte 1998). Using data from the Michigan Corpus of Academic Spoken English (MICASE), I assess the predictivity of various factors for the appearance of nonprestige there's , including the novel factor of discourse type. Two binary logistic regression models are developed to model the production of existentials. In both models, highly predictive factors included the type of determiner that appeared in the postcopular NP, the age of the speaker, and crucially, the type of discourse – monologic, interactive, or mixed – in which speakers were engaged. A “mixed-effect” (Baayen, Davidson et al., submitted) logistic regression model provided a better fit to the data than the standard logistic regression model used in previous studies, highlighting the importance of idiolectal variation in the production of existentials. Implications for syntactic theories of the existential construction are discussed.