Date of Award


Degree Type


Degree Name

Doctor of Philosophy in Clinical Psychology


Clinical Psychology



First Advisor

Mark Robbins


The transtheoretical model (TTM) is a comprehensive theory of health behavior change that has informed a wide range of health promotion interventions. Despite substantial empirical support for the TTM, our understanding of the mechanisms of behavior change is primarily guided by cross-sectional research. Considerably fewer studies have examined longitudinal relationships between TTM constructs with methods comparable to cross-sectional models. The overarching goal of the present study was to improve our understanding of longitudinal relationships between Stage of Change, Decisional Balance, and Self-Efficacy. Kidney transplant decision-making was used to exemplify longitudinal patterns through secondary data from the trial Your Path to Transplant. Across three study objectives, effect size estimates and behavioral predictors were performed to measure magnitudes of change in Decisional Balance (DB) and Self-Efficacy (SE) and detect characteristics that promote readiness for change.

Transtheoretical constructs were measured at the baseline, four-month, and eight-month timepoints among a sample of kidney patients (N = 815). Objectives one and two employed repeated measures Hedges’ g effect size estimates and 95% confidence intervals to quantify the amount of change in DB (Pros and Cons) and SE from earlier to later timepoints. First, a selection of 534 participants were grouped by Forward, Stable, and Backwards trajectories of Stage movements (e.g., PC-A, A-A, or A-PC). Second, groups were formed among participants who showed substantial change in three construct groups: Increased Pros, Decreased Cons, and Increased Confidence (N = 571). In the third objective, a logistic regression analysis tested whether completion of eight behavioral variables (LDKT Steps) at baseline significantly differentiated individuals who moved to Action versus Pre-Action (N = 301).

Effect size findings among groups of Forward Stage transitions provided partial longitudinal support for cross-sectional models within the context of LDKT decision-making. Consistent with cross-sectional models, movement to Action involved increased Pros, decreased Cons, and increased SE. Further, effect sizes for Cons were smallest in adjacent Stage movement and increased proportionately among transitions of two and three Stages. While Pros are commonly understood as the strong principle of change, effect size findings across groups of Stage transitions and construct change suggest that successful behavior change is most strongly driven by Cons. Results are within the context of kidney transplant decision-making and are also in recognition that cross-sectional models are measured with different methods than longitudinal models. Previous findings suggest a difference of -0.50 SD, while a difference of -1.11 SD was demonstrated longitudinally. Lastly, previous engagement in eight common behaviors involved in pursuing transplant significantly predicted movement to Action, with the strongest predictors indicative of greater readiness for pursuing transplant.

Available for download on Friday, July 15, 2022