Variance estimation in two-step calibration for nonresponse adjustment

Rota and Laitila (2015) suggest an alternative two-step calibration estimation resulting from combining two approaches, i.e., linear (Särndal Lundström, 2005) propensity score (Chang Kott, 2008), when the functional form of response probability is assumed to be known. The first step focuses on estimating this function second total a survey variable. This paper extends these previous findings by deriving approximate variance expression suggesting estimator for estimator. also justifies use sample-level auxiliary information in estimation, deferring population-level estimation. Keywords: Auxiliary information, Calibration, Nonresponse, Response probability, Two-step, Variance