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Increasing the credibility of the twin birth instrument
Author(s) -
Farbmacher Helmut,
Guber Raphael,
Vikström Johan
Publication year - 2018
Publication title -
journal of applied econometrics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.878
H-Index - 99
eISSN - 1099-1255
pISSN - 0883-7252
DOI - 10.1002/jae.2616
Subject(s) - fertility , dizygotic twins , credibility , construct (python library) , dizygotic twin , economics , econometrics , demographic economics , twin study , medicine , obstetrics , computer science , population , heritability , biology , environmental health , genetics , programming language , political science , law
Summary Twin births are an important instrument for the endogenous fertility decision. However, twin births are not exogenous either as dizygotic twinning is correlated with maternal characteristics. Following the medical literature, we assume that monozygotic twins are exogenous, and construct a new instrument, which corrects for the selection although monozygotic twinning is usually unobserved in survey and administrative datasets. Using administrative data from Sweden, we show that the usual twin instrument is related to observed and unobserved determinants of economic outcomes, while our new instrument is not. In our applications we find that the classical twin instrument underestimates the negative effect of fertility on labor income. This finding is in line with the observation that high earners are more likely to delay childbearing and hence have a higher risk to get dizygotic twins.