Background Substance use decreases in pregnancy but little prospective data are available on the rates of abstinence and relapse for specific substances. This study compared rates of abstinence in pregnancy and relapse postpartum for nicotine cigarettes, alcohol, marijuana, and cocaine. Methods...

The functional coefficient regression models assume that the regression coefficients vary with some "threshold" variable, providing appreciable flexibility in capturing the underlying dynamics in data and avoiding the so-called "curse of dimensionality" in multivariate nonparametric estimation....

A frequent problem in longitudinal studies is that subjects may miss scheduled visits or be assessed at self-selected points in time. As a result, observed outcome data may be highly unbalanced and the availability of the data may be directly related to the outcome measure and/or some auxiliary...