Further, the primary source of maternal Tofacitinib CP-690550 SDP data comes from reports within 1 year of the child��s birth, addressing a limitation of long recall times discussed elsewhere (Kandel & Udry, 1999; O��Callaghan et al., 2006). Other exposure to tobacco smoke was not assessed which might occur from father or other family members smoking; such exposure may exacerbate the genetic, physiological, and social mechanisms of intergenerational transmission. We also did not account for other methods of nicotine use, such as smokeless tobacco or smoking of tobacco through means other than cigarettes (e.g., pipe, cigar). These will be likely to bias our results in the direction of the null hypothesis as children who were exposed to nicotine will have been classified incorrectly as nonsmokers.

Some issues arise with the sample. The sample was large, but even such a large sample led to relatively small numbers of individuals in, for example, the early experiment group with a sample of 127. This small sample size has limited statistical power in analyses including this group. The data on smoking are recorded biennially; therefore, our trajectories cannot capture short-term fluctuations in cigarette behavior but rather describe overarching patterns of youth smoking across adolescence and young adulthood. Finally, due to the cohort structure of the NLSY79-CYA sample, the most complete portion of data covers the period age 14�C16 and thus may be less representative of smoking patterns in early adulthood than have been described in previous population representative studies The small size of the mediation effect, relative to the direct effect of maternal smoking (of any class) means that the result is vulnerable to omission of control variables that are precursors to maternal smoking, child smoking, and child behavior problems.

Although we included a wide range of control variables, additional unmeasured covariates that are associated with all three variables of interest would create an artifactual mediation effect. The results of this study provide a rigorous test of the mediation through behavior problems hypothesis and suggest that the mechanism of intergenerational transmission of smoking via SDP follows a more direct route, potentially via a physiological mechanism. However, maternal smoking after Entinostat pregnancy seemed to be associated with youth smoking, at least in part, because of a mediation effect of problem behavior.