Controlled Variance: AI's Edge as Reduced Dispersion

Jabarian & Henkel (arXiv 2607.28222): a pre-registered natural field experiment randomizing 70,884 job applicants between AI voice interviewers and human recruiters — offer rate 8.70%→9.73% (+12%), job starts +18%, one-month retention +18%, no productivity decline, with humans making every hiring decision in both arms. The mechanism the authors name is *controlled variance*: the AI follows the firm's interview protocol more consistently (topic order τ 0.53 vs 0.33, question similarity 0.59 vs 0.43, significantly lower cross-interview variance) while still adapting per applicant and using *richer* vocabulary — AI wins by being less dispersed, not more capable. The wiki's only randomized causal estimate of AI substituting for a human in an expert conversational task