We evaluated demographic differences between diagnostic groups (SZ/SA vs. Control) using independent samples t-tests for continuous variables and chi-square tests for dichotomous variables. We did not detect differences between groups on age, racial categories, or attainment of high school diploma or GED (p > .05). Chi square analyses detected significant differences between groups with respect to gender, x2(1) = 4.77, p = .029, employment, x2 (1) = 8.25, p = .004, and receipt of public financial assistance, x2 (1) = 18.86, p < .001. Control smokers were more likely to be women. Control smokers were less likely to be unemployed or receiving public assistance than were those with SZ/SA - though there were very high rates of unemployment (76% for controls and 93% for those with SZ/SA) and receipt of public assistance (68% for controls and 96% for those with SZ/SA) in both groups.
We then evaluated the relationship between persistence and the demographic variables previously found to be related to diagnostic category (i.e., gender, employment, and receipt of public financial assistance). Independent samples t-tests indicated that males persisted in breath-holding significantly longer than females, t(147) = 2.83, p = .005, and females scored significantly higher than males on the 2-item Persistence Measure, t(147) = −2.11, p = 0.036 though mirror tracing and the TCIP were unrelated to gender (p > .05). Those receiving public assistance persisted for significantly less time on the mirror tracing task, t(147) = 2.92, p = .004, and scored significantly higher on the 2-item persistence scale, t(147) = −2.06, p = 0.041, than those not receiving public assistance. Those who were unemployed displayed a trend towards reduced persistence on the mirror tracing task as compared to those who were employed, t(148) = 1.97, p = .053. No other persistence measures were related to public assistance or employment.
We also evaluated differences in tobacco use between diagnostic categories (SZ/SA vs. control smokers). There were no differences between groups (p > .05) on number of serious quit attempts, length of longest cigarette abstinence, cigarettes smoked per day, or motivation to quit (though a statistical trend was found for motivation to quit favoring the Control group). Those with SZ/SA were, however, significantly more nicotine dependent based on the Fagerstrom Test for Nicotine Dependence (FTND; Heatherton et al., 1991
(147) = −2.13, p =
Differences in Persistence between SZ/SA and Control Smokers
We evaluated the relationship between the dependent variable, “persistence” and the independent variable, “diagnostic category” in four separate analyses of covariance (ANCOVA) for each of four persistence variables (i.e., mirror-tracing persistence, 2-item self-report persistence measure, Temperament and Characteristics Inventory – Persistence Scale (TCI-P), and breath-holding persistence). Covariates included FTND score, gender, and receipt of public assistance because these variables were significantly related to diagnostic category and persistence variables. The models included a gender X diagnostic category interaction term, but not a public assistance X diagnostic category interaction term because the latter would have too few participants in the cell reflecting those with SZ/SA but not receiving public assistance (n = 3). We applied a Bonferroni correction to all analyses.
Non-psychiatric control smokers demonstrated significantly greater persistence on the mirror tracing task, F(1,148) = 9.62, p = .002, and on the two-item Persistence Measure, F(1,148) = 5.22, p = .023 than did smokers with SZ/SA. We did not detect significant differences between groups for persistence as measured by the TCI-P, F(1,148) = .98, p = 0.32, or for breath-holding persistence, F(1,148) = .75, p = 0.39. We did not detect significant gender X disorder interactions for any of the persistence variables (all p > .05).
Persistence and Previous Quitting History
We also evaluated the relationship between persistence and past history of ability to maintain sustained abstinence from cigarettes. We conducted several 2 (Control vs. SZ/SA) X 2 (abstinence vs. no abstinence) analyses of variance. Abstinence intervals were retrospective and included four dichotomous items: at least 48-hours, at least one-week, at least one-month, and at least one-year of abstinence. The four persistence variables were: Mirror-tracing persistence, Two-item self-report persistence, Temperament and Characteristics Inventory – Persistence Scale, and Breath-holding persistence.
We found significantly greater mirror tracing persistence among participants reporting histories of abstinence for at least one-week, F(1,148) = 3.98, p = .048, and at least one-year, F(1,148) = 6.03, p = .02, as compared to those unable to maintain abstinence for those time periods. We also detected statistical trends indicating greater mirror tracing persistence among participants reporting histories of abstinence for at least 48-hours, F(1,147) = 3.59, p = .06, and at least 30-days, F(1,148) = 3.69, p = .057, as compared to those unable to maintain abstinence for those time periods. We were unable to detect a significant relationship between persistence and prior greatest length of abstinence at any time period (i.e., 48-hours, one-week, one-month, or one-year) when persistence was measured by breath-holding, or by scores on the TCI-P or two-item Persistence Measure (all p > .05). The interaction term was non-significant for all measures of persistence for all for abstinence durations (p > .05).