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This study describes the benefits and challenges of meta-analyses of single-case design research using multilevel modeling. The researchers illustrate procedures for conducting meta-analyses using four-level multilevel modeling through open-source R code. The demonstration uses data from multiple-baseline or multiple-probe across-participant single-case design studies (n = 21) on word problem instruction for students with learning disabilities published between 1975 and 2023. Researchers explore changes in levels and trends between adjacent phases (baseline vs. intervention and intervention vs. maintenance) using the sample data. The researchers conclude that word problem solving of students with learning disabilities varies based on the complexity of the word problem measures involving single-word problem, mixed-word problem, and generalization questions. These moderating effects differed across adjacent phases. These findings extend previous literature on meta-analyses methodology by describing how multilevel modeling can be used to compare the impacts of time-varying predictors within and across cases when analyzing single-case design studies. Future researchers may want to use this methodology to explore the roles of time-varying predictors as well as case or study-level moderators. (PsycInfo Database Record (c) 2024 APA, all rights reserved).
RESUMO
RATIONALE: Chronic marijuana use has been associated with impairments of learning, memory, and executive functions. Little is known, however, about the effects of marijuana use on other cognitive domains, such as decision-making, which are thought to play an important role in addiction and drug abuse. OBJECTIVES: The purpose of the present study was to determine if long-term heavy marijuana users employ different decision-making strategies than individuals with minimal marijuana exposure. METHODS: Volunteers were assigned to a cannabis (n = 10) or control group (n = 10) based upon history of prior marijuana use. Demographic and neuropsychological variables were evaluated, and a decision-making task--the gambling task (GT) was administered. RESULTS: Although few demographic and neuropsychological differences were noted between groups, marijuana users made more decisions that led to larger immediate gains despite more costly losses than controls. CONCLUSIONS: These data suggest that long-term heavy marijuana users may have specific deficits in the ability to balance rewards and punishments that may contribute to continued drug-taking behavior. It is unknown, however, whether the basis for such deficits might be attributed directly to marijuana exposure or pre-existing genetic or behavioral differences.
