Please use this identifier to cite or link to this item: https://hdl.handle.net/10419/163543 
Year of Publication: 
2016
Series/Report no.: 
ISER Working Paper Series No. 2016-17
Publisher: 
University of Essex, Institute for Social and Economic Research (ISER), Colchester
Abstract: 
Twin births are often construed as a natural experiment in the social and natural sciences on the premise that their occurrence is quasi-random. We present new population-level evidence challenging this premise. Using data on about 18 million births in 72 countries, we find that maternal condition is positively associated with twin birth. Thus studies using twins to instrument fertility will under-estimate impacts of fertility on parental investments and women's labour supply. This is pertinent given recent research indicating these relationships are weak. Using developing country and US data, we demonstrate the bias and estimate bounds on the true parameter.
Subjects: 
twins
fertility
maternal health
miscarriage
quantity-quality trade-off
parental investment
bounds
JEL: 
J12
J13
C13
D13
I12
Document Type: 
Working Paper

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