Patterns of Electronic Portal Use among Vulnerable Patients in a Nationwide Practice-based Research Network: From the OCHIN Practice-based Research Network (PBRN) - Wallace, LS; Angier, H; Huguet, N; Gaudino, JA; Krist, A; Dearing, M; Killerby, M; Marino, M; DeVoe, JE (Journal of the American Board of Family Medicine: JABFM, 2016)