These findings are discussed below. Survey Participation Effect Meaningful interpretation of the selleck chem findings may benefit from some discussion of the role of survey participation effect evident in this paper. Consistent with other studies showing that being surveyed can induce practice/learning effect on subsequent reports (Duncan & Kalton, 1987; Karlamangla et al., 2009; Thompson, Boudreau, & Driezen, 2005), this study clearly demonstrates that participation in a survey is acting as an intervention in itself producing a marked initial downward effect on reported cigarette consumption. One would expect that the longer the participation in the study, the greater the influence of the surveying effect, but we found no such evidence as the rate of decline was similar across the various cohorts with different lengths of participation in the study suggesting that the survey participation effect was limited to the initial period of participation and not beyond.

The survey effect appears largely to be due to increased attempts to quit between assessment Waves 1 and 2, presumably stimulated by increased awareness of the harms of smoking following participation in the ITC Survey. The effect of quitting activity on consumption is consistent with our previous findings that a failed quit attempt can help keep cigarette consumption at a low level upon resumption (Yong et al., 2008). The decline could also reflect an attempt by continuing smokers (not interested in quitting) to reduce their consumption after being stimulated by the survey to think more about the harm of smoking.

Regardless of the actual mechanism, survey participation appears to have a positive immediate incidental effect on continuing smokers�� daily cigarette consumption. Linear Decline in CPD The finding of a linear decline over the study period (2002�C2007) in reported daily cigarette consumption of continuing smokers suggests that in all four countries studied here, there is a secular trend toward reduced smoking among those who are unwilling or unable to quit smoking. The trend toward reduced smoking could either be due to external coercion resulting from comprehensive tobacco control policies and programs, such as increased smoke-free places (Pierce, Messer, White, Cowling, & Thomas, 2011), or an intentional act on the part of the smokers for the purpose of harm reduction (Gilpin & Pierce, 2002; Hughes & Carpenter, 2005). The former explanation seems less plausible, given that the cohort of daily smokers newly recruited at each survey wave did Brefeldin_A not show any evidence of differences in baseline CPD and also there was no known extensive implementation of smoke-free policies in the four studied countries during the study period.