Evidence that psychological stress is causally related to birth weight comes from quasi-experimental studies that exploit natural disasters (Glyn et al., Conley and Bennett (2000) use panel data (PS1D) from the US and apply grandmother fixed effects to control for unobservable family factors to estimate the heritability of child birthweight. They find that a child born to a mother who was born with low birthweight (LBW) is 6.6 times as likely to be of LBW compared to a relative whose mother was not born with LBW. Currie and Moretti (2007) revisit the same question using individual birth records from California and show substantial intergenerational correlation in health i.e. that women who were low birth weight are more likely to deliver low birth weight infants, and this effect is greater if the women are living in a low income neighborhood.