The dynamic structural equation modeling (DSEM) framework incorporates hierarchical latent modeling (HLM), structural equation modeling (SEM), time series analysis (TSA), and time-varying effects modeling (TVEM) to model the dynamic relationship between latent and observed variables. To model the functional relationships between variables, a Gaussian process (GP), by definition of its covariance function(s), allows researchers to define Gaussian distributions over functions of input variables. Therefore, by incorporating GPs to model the presence of significant trend in either latent or observed variables, this dissertation explores the adequacy and performance of GPs in manipulated conditions of sample size using the flexible Bayesian analysis approach. The overall results of these Monte Carlo simulation studies showcase the ability of the multi-output GPs to properly explore the presence of trends. Also, in modeling intensive longitudinal data, GPs can be specified to properly account for trends, without generating significantly biased and imprecise estimates.

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This study investigated how social media use is related to body esteem (particularly weight satisfaction and muscularity importance) in adolescents. We conducted a 17-day Ecological Momentary Assessment study among 183 adolescents (12–17 years, 58% girls). Each adolescent reported on his/her social media use, weight satisfaction, and muscularity importance four times per day (68 assessments per participant; 6,863 completed in total). Using a person-specific, N=1 method of analysis (Dynamic Structural Equation Modeling), we found that at the between-person level, social media use is not associated with lower satisfaction with one’s weight and greater importance of looking masculine. At the within-person level, we found a significantly negative association for weight satisfaction and a significantly positive association for muscularity importance. For weight satisfaction, 76% of adolescents experienced no or very small effects as a result of SMU, 2% experienced positive effects, and 22% experienced negative effects. Regarding muscularity importance, 89% experienced no or very small effects of SMU on muscularity importance, 10% experienced positive effects, and 1% experienced negative effects. There is little evidence of gender differences in the effect of social media on body esteem in our sample.