Table S2.

Construction of oversample

	Percent Republican
Practice size	0–20	20–80	80+	Total
Small (1–3)	5,600	1,253	5,180	12,033
Medium (4–10)	348	754	151	1,253
Large (11+)	205	187	0	392
Total	6,153	2,194	5,331	13,678

We derived our sample from 13,678 party-registered physicians with mailable residential addresses. We stratified the sample by practice size and practice percent Republican. Practice size here is determined by the number of Democratic and Republican physicians in our sample. For midsized mixed-partisan practices (indicated in bold), we sampled all 754 physicians. We sampled 6% of all other cells to generate an overall sample of 1,529 physicians.