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Author: Jackson, Nicholas J.
Resulting in 1 citation.
1. Jackson, Nicholas J.
The Design, Implementation, and Evaluation of Accelerated Longitudinal Designs
Ph.D. Dissertation, University of Southern California, 2018
Cohort(s): NLSY97
Publisher: ProQuest Dissertations & Theses (PQDT)
Keyword(s): Alcohol Use; Drug Use; Modeling; Monte Carlo

Permission to reprint the abstract has not been received from the publisher.

Longitudinal designs are the gold standard for researchers studying within-subject changes in age-related development. These designs are typically conducted using a single cohort followed for a fixed period of time. However, single-cohort designs often necessitate a lengthy time commitment from participants, sponsors, and researchers which make them vulnerable to greater attrition and even premature termination. The time commitment for these designs also means that the results may be obsolete by the time they are published, particularly if the outcomes under study are sensitive to generational differences. Bell (1953) proposed the use of an Accelerated Longitudinal Design (ALD) as a means to generate age-based trajectories over a shortened duration to combat these issues. In the ALD multiple birth-cohorts are studied simultaneously in a longitudinal fashion with overlap in the age distributions between the cohorts. In this manner the same age span may be studied while reducing the number of measurements per participant, the study duration, and study costs. These designs also allow for the modeling of between-cohort differences, which are important for researchers interested in developing age-based trajectories that generalize to multiple cohorts. While models that incorporate cultural influence are increasingly relevant, there has not yet been widespread adoption of these designs. Part of the hesitancy to use ALDs stems from their unfamiliarity, as few methodological papers have demonstrated the efficacy of these designs for studying development. We propose the use of cost equations to utilize the cost-savings of the ALD to determine sample sizes that are of equal cost to a single-cohort design. The use of an equal cost sample size allows for ALDs to have N’s that are 10-85% larger than in the single-cohort design, thereby offsetting the potential loss of power in the ALD. We subsequently utilize Monte Carlo simulation methods to demonstrate how the statistical power and bias in the ALD is comparable to that of the single-cohort design for both linear and nonlinear models and discuss considerations for when between-cohort differences in development are present. Lastly, we use data from the National Longitudinal Survey of Youth (NLSY 1997) to demonstrate the ability of an ALD to capture both within-person and between-cohort variability in marijuana and tobacco use from the ages of 12 to 32. We additionally discuss considerations for the modeling of cohort membership and alternate strategies for cohort inclusion. Results from the simulations and in the NLSY suggest that ALDs should be the preferred longitudinal design for researchers studying age-related development.
Bibliography Citation
Jackson, Nicholas J. The Design, Implementation, and Evaluation of Accelerated Longitudinal Designs. Ph.D. Dissertation, University of Southern California, 2018.