Third variable analysis: application to causal sequences among nutrient intake, maternal weight, birthweight, placental weight, and gestation.

We applied a set of procedures, aimed at enhancing the strength of inferences about the direction of causal paths among variables measured at the same time, to foetal and maternal indices recorded at birth and collected for study of the Dutch famine of 1944/5. The analysis of three-variable sets yielded strong inferences about the relations among caloric intake, maternal weight, birthweight, placental weight, and length of gestation. These procedures constitute not only a useful preliminary to the construction of multivariate path models, but produce useful results in their own right.