Np.OR: an S-Plus function for pointwise nonparametric estimation of odds-ratios of continuous predictors

Calculating odds ratios (OR) and corresponding confidence intervals (CI) for exposures that have been measured using a continuous scale, presents important limitations in the traditional practice of epidemiology. Our objective is to describe an S-Plus function, that we called np.OR, that allows the computation of the pointwise estimates of the ORs as well as their corresponding CIs of continuous predictors introduced nonlinearly in a generalised model. The function can also be generalised to compute the pointwise estimates of categorical predictors that were introduced nonlinearly. To illustrate usage of the program we analyse the relationship between ambient temperature and total mortality in Barcelona for the period 1991-1995, while controlling for observed and unobserved confounders.