Timberlake David S, Huh Jimi, Lakon Cynthia M
Department of Population Health and Disease Prevention, Program in Public Health, University of California, Irvine, 100 Theory, Suite 100, Irvine, CA 92697-7555, USA.
Nicotine Tob Res. 2009 Apr;11(4):455-62. doi: 10.1093/ntr/ntp008. Epub 2009 Mar 23.
The contentious debate over the promotion of Swedish snus, a form of moist snuff, as an alternative to cigarettes has often focused on the product's potential as a gateway to smoking. Findings from prospective studies in the United States have suggested that smokeless tobacco (SLT) is a significant predictor of smoking onset, before and after adjustment for baseline covariates. Use of conventional regression methods in these studies may have resulted in biased parameter estimates, arising from imbalanced covariate distributions in the users and nonusers of SLT. An alternative approach, which has been used widely in the econometric literature, matches exposure or treatment levels on the basis of the propensity score distribution.
Using this approach, we matched current SLT users from the National Longitudinal Study of Adolescent Health with nonusers (496 pairs) and followed them from adolescence into young adulthood for determination of smoking status.
Prior to matching, the unadjusted risk of becoming a daily smoker was significantly greater for the SLT users compared with nonusers (n = 10,820; range of relative risk = 1.3-2.0, p < .001). However, after pairing individuals on propensity score, we found no evidence for an increased risk of smoking among the SLT users.
Baseline differences in the risk factors for smoking likely account for the association between the two tobacco products.
关于推广瑞典口含烟（一种湿鼻烟）作为香烟替代品的争论一直聚焦于该产品作为吸烟入门途径的可能性。美国前瞻性研究的结果表明，在对基线协变量进行调整前后，无烟烟草（SLT）都是吸烟开始的重要预测因素。这些研究中使用的传统回归方法可能导致参数估计存在偏差，这是由于SLT使用者和非使用者协变量分布不均衡所致。计量经济学文献中广泛使用的另一种方法是根据倾向得分分布匹配暴露或治疗水平。
采用这种方法，我们将来自青少年健康全国纵向研究的当前SLT使用者与非使用者进行匹配（496对），并跟踪他们从青春期到青年期，以确定吸烟状况。
在匹配之前，与非使用者相比，SLT使用者成为每日吸烟者的未调整风险显著更高（n = 10,820；相对风险范围 = 1.3 - 2.0，p < .001）。然而，在根据倾向得分配对个体后，我们没有发现SLT使用者吸烟风险增加的证据。
吸烟风险因素的基线差异可能是这两种烟草产品之间关联的原因。
