In an online rapid response letter published in the journal Pediatrics, Dr. Joel Moskowitz, Director of the Center for Family and Community Health at the UC Berkeley School of Public Health, suggests an alternative explanation for the observed association between exposure to smoking in movies and smoking initiation among adolescents.
Dr. Moskowitz reports in the letter the results of studies he has done showing that children tend to under-report smoking in telephone surveys when a parent is listening to, or present during, the interview. Among children ages 12-14 years, 57% reported that a parent heard them being interviewed. The self-reported prevalence of ever smoking/puffing was only 9% for those who reported that a parent heard the entire interview but was 20% for those who reported a parent being home but not hearing the interview and was 27% for those who did not have a parent home during the interview.
The importance of this result for the present study is that children whose parents are protective to the extent that they do not allow their children to see R-rated movies (which have higher numbers of smoking portrayals) may also be protective to the extent that they are present during the interview of their children:
"The interpretation of results from the authors' studies of exposure to smoking in movies is of particular concern because children who reported low exposure to smoking in movies (i.e., those whose parents did not allow them to see R-rated movies) may have more protective parents who are more likely to be present during their child's telephone interview compared to children who reported high exposure to smoking in movies. If this were true, and if parental presence during the interview caused these children to under-report smoking initiation, then the results of the authors' studies could be explained by this confounding."
The Rest of the Story
This seems to be an important potential threat to the validity of the conclusion of the studies linking exposure to smoking in movies with a higher risk of smoking initiation. Under-reporting of smoking due to parental presence is indeed a plausible confounder because it is clearly associated with the outcome (self-reported smoking) and is likely associated with the exposure (being "allowed" by parents to see R-rated movies which contain more smoking), and because the magnitude of the reported effect on self-reported smoking behavior is so large.
The presence of a potential confounder does not negate or render invalid the conclusions of the study; it merely suggests a potential alternative explanation for the study findings that must be considered. Hopefully, this potential explanation can be addressed in future research.
I can't help but add that another potential confounding factor is differences in parental protectiveness itself, independent of any effect of protectiveness on interview presence. Parents who allow their kids to see R-rated movies would certainly seem to have a different level of protectiveness and might not this factor itself be related in some way to smoking initiation?
One potential mediator for this relationship is the association between protectiveness and perceived parental disapproval of smoking, which was shown to be a significant inhibitor of smoking initiation by the same researchers who reported the movie exposure - smoking initiation link.
Of note, the original research paper did indeed control for parenting style (using an authoritative parenting index); however, it is unclear to me whether this measure truly can account adequately for the range of differences in parenting between parents of kids who are allowed or not allowed to view R-rated movies.
The rest of the story is not that there is anything wrong with the conclusion that exposure to smoking in movies seems to be a risk factor for smoking initiation. Instead, my conclusion is that there are some plausible alternative explanations for this observed association, and because of this, it seems premature to draw a definitive conclusion. But far more importantly, it seems premature, for sure, to be providing precise quantitative estimates of the number of kids who start smoking due to seeing smoking in movies. I think a little more respect for the science, and a little less urgency to support an agenda, is in order.