Poisson Growth Mixture Modeling of Intensive Longitudinal Data: An Application to Smoking Cessation Behavior.

Intensive longitudinal data (ILD) have become increasingly common in the social and behavioral sciences; count variables, such as the number of daily smoked cigarettes, are frequently-used outcomes in many ILD studies. We demonstrate a generalized extension of growth mixture modeling (GMM) to Poisson-distributed ILD for identifying qualitatively distinct trajectories in the context of developmental heterogeneity in count data. Accounting for the Poisson outcome distribution is essential for correct model identification and estimation. In addition, setting up the model in a way that is conducive to ILD measures helps with data complexities - large data volume, missing observations, and differences in sampling frequency across individuals. We present technical details of model fitting, summarize an empirical example of patterns of smoking behavior change, and describe research questions the generalized GMM helps to address.

Fear of litigation may increase resuscitation of infants born near the limits of viability.

OBJECTIVES: To explore how fear of litigation influences neonatal treatment decisions. STUDY DESIGN: In a mailed survey, we presented a hypothetical vignette of a premature infant to 1000 neonatologists. We asked them to estimate prognosis, indicate appropriate intervention, and respond to parental treatment requests. Subjects were randomly assigned to receive one of two questionnaires, "litigious" or "nonlitigious," which differed only in the description of the infant's parents. RESULTS: The response rate was 63.0%. The vast majority of respondents deferred to parental requests rather than adhering to their best judgment. They deferred whether or not parents requested treatment and whether or not parents were described as litigious (P <.0001). Among those respondents who shifted their resuscitation opinion after parental introduction, respondents to the nonlitigious version were more likely to shift their opinion from "treat" to "do not treat" after parental requests to "use your best judgment" (P <.042). The influence of parental litigiousness was primarily seen among neonatologists who thought that the infant's prognosis was dismal (P <.044). CONCLUSIONS: There is a strong disposition among neonatologists toward respecting parental wishes. This disposition is stronger when neonatologists are given additional reason to be concerned about litigation.