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Double Robustness in Estimation of Causal Treatment Effects

Double Robustness in Estimation of Causal Treatment Effects

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E<br />

5. Doubly Robust Estimator<br />

� �<br />

{Z − e(X)}<br />

{Y1 − m1(X, α1)}<br />

e(X)<br />

� � �<br />

{Z − e(X)}<br />

�<br />

= E E<br />

{Y1 − m1(X, α1)} �<br />

e(X)<br />

� Y1,<br />

��<br />

X<br />

�<br />

� �<br />

{Z − e(X)} �<br />

= E {Y1 − m1(X, α1)} E<br />

�<br />

e(X) � Y1,<br />

��<br />

X<br />

�<br />

= E {Y1 − m1(X, α1)} {E(Z|Y1,<br />

�<br />

X) − e(X)}<br />

e(X)<br />

�<br />

�<br />

{E(Z|X) − e(X)}<br />

= E {Y1 − m1(X, α1)}<br />

e(X)<br />

�<br />

�<br />

{e(X) − e(X)}<br />

= E {Y1 − m1(X, α1)} = 0<br />

e(X)<br />

(1) uses no unmeasured confounders<br />

<strong>Double</strong> <strong>Robustness</strong>, EPID 369, Spr<strong>in</strong>g 2007 30<br />

(1)

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