Key Findings
NIM Trend by Size Decile
Mean net interest margin by quarter, grouped by bank size decile (1 = smallest, 10 = largest). 8,032 banks, 64 quarters, 2010–2025.
Each line represents one size decile of banks. The persistent gap between small-bank (top) and large-bank (bottom) lines reflects the cross-sectional size penalty.
The core finding: larger banks have lower NIM both cross-sectionally and within-bank over time. But this is not the full story — large banks offset the NIM penalty with higher fee income and noninterest revenue, producing higher overall ROA. The NIM penalty is real but the earnings model is different, not worse.
Time variation matters: in rolling 20-quarter fixed-effects windows, the within-bank size penalty weakens to about −0.033 in the mid-2010s, steepens to about −0.144 in 2019–2024, and then eases in the latest window.
Cross-Section: NIM vs. Bank Size
Binscatter of average NIM against average log assets (20 equal-sized bins). The downward slope visualizes the between-bank size penalty.
Models & Results
Nine result sections from baseline fixed-effects through rate-cycle heterogeneity, acquisition event studies, threshold crossings, rolling time-varying coefficients, and the extension battery. Full coefficient tables with significance stars, confidence intervals, and dynamic interpretation notes.
Data & Distributions
Distribution plots for assets, NIM, and growth. Size-decile summary table. Complete data-source documentation and reproducibility notes for the full FDIC-based pipeline.
Reproducibility
Every data source is free and federally published. Every download is scripted. The full pipeline — from raw FDIC data through panel construction, model estimation, and robustness battery — can be reproduced from scratch. See the GitHub repository for setup instructions.