The use of regression models for medians when observed outcomes may be modified by interventions.

Some outcomes used in epidemiological studies and clinical trials are prone to modification by interventions, for example, individuals with high blood pressure are likely to receive antihypertensive medication. Often the scientific interest is in the relationship of covariates (exposures or randomized treatment) to the outcomes that would have been observed in the absence of intervention. We compare three approaches to the analysis of such data: ignoring the intervention; excluding individuals who receive the intervention, and assuming that individuals who receive the intervention have underlying outcomes above the median.

The increase in very-low-birthweight infants in Germany: artefact or reality?

Earlier findings have shown that after unification with the Federal Republic of Germany (FRG) in October 1990 the proportion of very-low-birthweight infants in the former German Democratic Republic (GDR) increased. This study seeks to explore this observation in more detail at the regional level. The analysis of aggregate data of live births in Germany between 1991 and 1997 shows an increasing proportion of very-low-birthweight infants as well as a general trend towards heavier babies in both east and west.