Abstract
Ecological momentary assessments (EMAs) are useful for understanding both between- and within-subject dynamic changes in smoking and mood. Modeling 2 moods (positive affect [PA] and negative affect [NA], PA and NA) simultaneously will better enable researchers to explore the association between mood variables and what influences them at both the momentary and subject level. The EMA component of a natural history study of adolescent smoking was analyzed with a bivariate location-scale mixed-effects model. The proposed model separately estimates the between- and within-subject variances and jointly models the 2 mood constructs. A total of 461 adolescents completed the baseline EMA wave, which resulted in 14,105 random prompts. Smoking level, represented by the number of smoking events on EMA, entered the model as 2 predictors: one that compared nonsmokers during the EMA week to 1-cigarette smokers, and the second one that estimated the effect of smoking level on mood among smokers. Results suggest that nonsmokers had more consistent positive and negative moods compared to 1-cigarette smokers. Among those who smoked, both moods were more consistent at higher smoking levels. The effects of smoking level were greater for NA than for PA. The within-subject association between mood constructs was negative and strongest among 1-cigarette smokers; the within-subject association between positive and negative moods was negatively associated with smoking. Mood variation and association between mood constructs varied across smoking levels. The most infrequent smokers were characterized with more inconsistent moods, whereas mood was more consistent for subjects with higher smoking levels.
Highlights
Ecological momentary assessments (EMA) are useful in understanding both between and within subject dynamic changes in smoking and mood
EMA methods yield data that are clustered within subjects and should be analyzed by methods that take into account the correlated observations
We propose to simultaneously model two mood states, Positive Affect (PA) and Negative Affect (NA), as they relate to smoking in adolescents
Summary
Ecological momentary assessments (EMA) are useful in understanding both between and within subject dynamic changes in smoking and mood. Many studies collect information on multiple outcomes (e.g., smoking level, withdrawal symptoms, and self-efficacy ratings). These outcomes are usually measured concurrently and repeatedly within each subject over time. One could examine how craving and self-efficacy for quitting change in tandem These multiple outcomes induce two types of associations: (1) at the subject level – association between the subjectaverage levels of outcomes, called between-subject (BS) covariance; and (2) at the momentary level – within-subject association for two outcomes at the measurement level, called within-subject (WS) covariance. The covariance of the random effects and the covariance of the error terms can themselves be modeled by separate linear models This helps to investigate how the associations between the outcomes change for different population subgroups or different treatment conditions. The association between two outcomes may vary by sex, age, racial group, or by exposure to different treatments
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