Identification in Regressions with Missing Covariates

Identification in Regressions with Missing Covariates -...

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Unformatted text preview: Identi&cation on Regressions with Missing Covariate Data & Esteban M. Aucejo y Federico A. Bugni z V. Joseph Hotz x February 8, 2010 Abstract This paper examines the problem of identi&cation and inference on parametric models when there are missing data, with special focus on the case when covariates, denoted by X , are missing. Our econometric model is given by a conditional moment condition implied by the assumption that X is strictly exogenous. At the same time, we assume that the distribution of the missing data is unknown. We confront the missing data problem by adopting a worst case scenario approach. We characterize the sharp identi&ed set and argue that this set is usually prohibitively complex to compute or to use for inference. Given this di culty, we consider the construction of outer identi&ed sets (that is, supersets of the identi&ed set) that are easier to compute and can still provide a characterization of the parameter of interest. Two di/erent outer identi&cation strategies are discussed. Both of these strategies are shown to contain non-trivial identifying power and are relatively easy to compute and to be used for inference. Keywords: Missing Data, Missing Covariate Data, Partial Identi&cation, Outer Identi&ed Sets. JEL Classi&cation Codes: C01, C10, C20, C25. & Thanks to Arie Beresteanu for useful comments and discussions. Any and all errors are our own. y Department of Economics, Duke University. Email: esteban.aucejo@duke.edu. z Department of Economics, Duke University. Email: federico.bugni@duke.edu. x Department of Economics, Duke University, NBER and IZA. Email: hotz@econ.duke.edu. 1 Introduction The problem of missing data is a ubiquitous problem in empirical social science research. When survey data is used to estimate an econometric model, the researcher is often faced with the situ- ation in which a dataset has missing observations on either outcome variables and/or covariates. Furthermore, one typically does not know the distribution of these missing data. This paper ex- amines the problem of identi&cation and inference on parametric models when there are missing outcome or covariate data. We focus on the case when covariates present missing observations, although we also consider the case in which outcome and covariates are simultaneously missing 1 . Our econometric model is as follows. We are interested in the true parameter value & that belongs to a parameter space & & R L that satis&es the following conditional moment condition, E ( Y f ( X;& ) j X = x ) = 0 ; for every x 2 S X (1) where Y : ! S Y & R denotes the outcome, X : ! S X & R K denotes the vector of covariates, f : R K R L ! R denotes a known function and S X and S Y denote the support of the outcome and the covariate, respectively. This econometric model can be equivalently expressed as follows, Y = f ( X;& ) + " (2) where " : ! R is a mean independent error term with its mean normalized to zero, E ( " j X = x ) = 0 ; for every x 2 S X...
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This note was uploaded on 12/26/2011 for the course ECON 245a taught by Professor Staff during the Fall '08 term at UCSB.

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Identification in Regressions with Missing Covariates -...

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