This code implements the thing that PREDMARG in SUDAAN does, as described in
- Graubard B, Korn E (1999) "Predictive Margins with Survey Data" Biometrics 55:652-659
- Bieler, Brown, Williams, & Brogan (2010) "Estimating Model-Adjusted Risks, Risk Differences, and Risk Ratios From Complex Survey Data" Am J Epi DOI: 10.1093/aje/kwp440