Standard 
Error
Number of providers at site
1 ---
a
2 0.070 *** 0.002
3-5 0.123 *** 0.003
6-10 0.183 *** 0.004
11 or more 0.226 *** 0.005
Site is part of multi-site group practice
No ---
a
Yes, 10 or fewer providers in group 0.058 *** 0.005
Yes, >10 providers in group 0.159 *** 0.003
Providers at site
Physicians only ---
a
Physicians and NPs or PAs 0.068 *** 0.002
NPs or PAs only -0.071 *** 0.009
Provider specialtymix at site
Specialist providers only ---
a
Primarycare providers only 0.063 *** 0.002
Mixed primarycare and specialists 0.035 *** 0.004
Site is owned bya hospital
No ---
a
Yes 0.049 *** 0.003
Site is affiliated with a health system
No ---
a
Yes 0.038 *** 0.003
Variance of PUMA randomeffect 0.063 +++ 0.001
N
Sites 261,973
PUMAs 2,068
***Coefficient estimate statisticallydifferent fromzero at p<0.001.
Coefficient
Appendix Table 1. Linear probabilityregression of EHRadoption 
amongU.S. ambulatoryhealth care sites
+++Likelihood ratio test ofrandomeffects versus linear regression statistically
significant at p<0.001.
aReferencecategory.