The response rate in the Introductory Psychology group was 91% (382 of 419 students enrolled in the course). Among students campus-wide, 1948 students were eligible to participate. Fourteen of these students were unreachable by email (e.g., invalid email address) and 457 students responded to the survey, yielding a response rate of 24% (457 of 1934). Of the 839 students who responded to the survey across both mechanisms, two students were excluded because of age (i.e., older than 24) and twelve students were excluded because of random responding or incomplete data (i.e., <10% of the survey completed). Thus, the final sample of student responders across both mechanisms is 825.
Ninety-five percent of non-responders (n = 1401) had a listed phone number, of which we attempted to contact approximately 6% (n = 84). Fifty-seven non-responders (4% of those with available phone numbers) were successfully contacted and interviewed. Due to the high response rate among the Introductory Psychology students, a non-responder sample was not gathered from this group.
Of the 825 participants in the current analyses, 68% were male and 32% were female. Participants were primarily Caucasian (91%), with an average age of 19.75 years (SD = 1.33, range = 18-24). Demographics of the sample reflect the overall school demographics. See for additional demographic information, by recruiting group. Participants in the Introductory Psychology courses were generally younger (t (823) = −10.64, p = .00) and more likely to be freshmen or sophomores than the campus-wide students, χ2 (4, N = 825) = 119.49, p <.01. Given the high correlation between participants' age and year in school (Spearman's rho = .88, p = .00), only participants' age is controlled in subsequent comparisons between these two groups.
Demographic Data for Study Participants
The subsample of non-responders was also compared to participants in the campus-wide group on available demographic data. Non-responders were generally older (t (501) = − 4.87, p = .00), more likely to be male, χ2 (1, N = 502) = 8.55, p = .003, and more likely to be upper classmen, χ2 (4, N = 503) = 19.16, p = .001, than campus-wide responders.
Comparisons Between Introductory Psychology Class and Campus-Wide Samples
Participants in the two groups did not differ significantly in reports of whether they had ever tried a cigarette [χ2 (1, N = 824) = .23, p = .63], were currently smoking [χ2 (1, N = 825) = .91, p = .34], or had smoked at least 100 cigarettes in their lifetime [χ2 (2, N = 823) = .36, p = .84]. Among students who were currently smoking, the groups did not differ significantly on nicotine dependence (t (86) = .79, p = .43). The two groups did, however, differ in their perceptions of cigarette smoking. The Introductory Psychology students reported higher smoker self-concept, more pros of smoking, and were more likely to view smoking as a method of negative affect reduction than the campus-wide students, even after controlling for participants' age (see ). Thus, although smoking behaviors did not differ significantly between the two groups, Introductory Psychology students tended to have more positive perceptions of smoking. Introductory Psychology students also reported drinking more per day, on average, than campus-wide students, but this difference was not significant once participants' age was taken into account.
Multivariate Analyses of Variance Examining Differences Between Introductory Psychology and Campus-Wide Students (N = 825)
A number of psychosocial factors were also examined. Introductory Psychology students reported significantly higher levels of depressive symptoms, anxiety, and perceived stress than their campus-wide counterparts. While group differences in perceived stress were reduced to nonsignificance (p > .05) after controlling for participants' age, differences in depression and anxiety were reduced but remained statistically significant (see ).
We also examined whether non-responders differed from the campus-wide responders in their smoking behaviors. Non-responders did not differ significantly in their reports of whether they had ever tried a cigarette [χ2 (1, N = 502) = .41, p = .52], or had smoked at least 100 cigarettes in their lifetime [χ2 (2, N = 501) = 3.78, p = .15], but non-responders were more likely to be current smokers than campus-wide survey responders [χ2 (1, N = 503) = 4.65, p = .03].