Table 1.

Comparison of Regression Discontinuity Design and Inverse-Probability–Weighted Marginal Structural Models as Causal Modeling Strategies for Initiation of Antiretroviral Therapy Among Persons With Human Immunodeficiency Virus Infection

Element of Study Design	Regression Discontinuity Design	Inverse-Probability–Weighted Marginal Structural Model
Causal question	The causal effect of immediate ART eligibility on mortality	The causal effect of ART initiation at entry to care on mortality
Effect estimated	Local treatment effect	Average causal effect
Key assumption	Potential outcomes are continuous at the threshold (continuity assumption)	No unmeasured confounding
Handling of confounding	Whether or not a person near the threshold presents to the clinic just above or just below the threshold is assumed to be random	Creating a pseudopopulation where treatment is random conditional on measured covariates
Statistical power relative to standard cohort methods	Strongly reduced	Reduced

Abbreviation: ART, antiretroviral therapy.