Sander Mismatch Hypothesis Empirical Tests

What the evidence says

The mismatch hypothesis holds that enrollment at a more-selective university may harm lower-testing students, especially those admitted through affirmative action. Zachary Bleemer's study of the University of California system tests this using Proposition 209, which changed which campuses lower-testing underrepresented-minority (URM) students enrolled at, as a quasi-experimental lever. The study's baseline findings are inconsistent with widespread mismatch. Two component results build that conclusion. First, before Prop 209, URM UC students did earn lower grades and were less likely to persist along introductory STEM course sequences than their non-URM peers — but this gap is largely explained by students' prior academic opportunities and preparedness, not by which campus they enrolled at. Second, when Prop 209 shifted URM students toward less-selective campuses, that shift did not improve their performance or persistence in STEM course sequences. Together these two results test the mismatch channel from both directions — selective enrollment is not shown to harm these students, and less-selective enrollment is not shown to help them — and neither supports the hypothesis. None of the retrieved claims report a quantified effect size (a percentage-point gap, a grade-point difference, or a persistence-rate change); the evidence here establishes direction (null / no improvement) but not magnitude.

Where the evidence splits

No contradictions in the current sources.

Thresholds and dose-response

No threshold established in the current sources.

Open empirical questions

• What is the quantified magnitude (grade-point, percentage-point, or persistence-rate difference) of the null effects reported — the current sources state direction but not size.
• Does the same null result hold outside STEM course sequences, or at institutions outside the UC system?
• What do the "multiple outcome measures" tracked through students' mid-30s show beyond STEM course performance and persistence — the current sources reference this longitudinal scope without detailing the additional measures.
• Does the mismatch hypothesis test replicate in other selective-admissions settings (for example, law school, which is where the hypothesis was originally debated)?