An IPW estimator for mediation effects in hazard models: with an application to schooling, cognitive ability and mortality

Large differences in mortality rates across those with different levels of education are a well-established fact. Cognitive ability may be affected by education so that it becomes a mediating factor in the causal chain. In this paper, we estimate the impact of education on mortality using inverse-probability-weighted (IPW) estimators. We develop an IPW estimator to analyse the mediating effect in the context of survival models. Our estimates are based on administrative data, on men born between 1944 and 1947 who were examined for military service in the Netherlands between 1961 and 1965, linked to national death records. For these men, we distinguish four education levels and we make pairwise comparisons. The results show that levels of education have hardly any impact on the mortality rate. Using the mediation method, we only find a significant effect of education on mortality running through cognitive ability, for the lowest education group that amounts to a 15% reduction in the mortality rate. For the highest education group, we find a significant effect of education on mortality through other pathways of 12%

Remarks on the structure-activity relationship of silver sulfanilamides

The biological activity of a series of 10 silver sulfanilamides is studied in relation to the physical parameters pK alpha, log K, and the aqueous solubility. None of the parameters demonstrate a simple relationship with the activity. A discussion of the significance of log K and the solubility in relation to the activity is given

PEAK TRACKING WITH A NEURAL NETWORK FOR SPECTRAL RECOGNITION

A peak tracking method based on a simulated feed-forward neural network with back-propagation is presented. The network uses the normalized UV spectra and peak areas measured in one chromatogram for peak recognition. It suffices to train the network with only one set of spectra recorded in one chromatogram of a sample to recognize the sample peaks in other chromatograms recorded in different mobile phases. The peak recognition method was used in a mixture design-based optimization of the separation of eight sulphonamides, some of which have very similar spectra. Even peaks in a cluster of four to five overlapping peaks could be recognized