This study investigated a method to evaluate mediational processes using latent growth curve modeling. The mediator and the outcome measured across multiple time points were viewed as 2 separate parallel processes. The mediational process was defined as the independent variable influencing the growth of the mediator, which, in turn, affected the growth of the outcome. To illustrate modeling procedures, empirical data from a longitudinal drug prevention program, Adolescents Training and Learning to Avoid Steroids, were used. The program effects on the growth of the mediator and the growth of the outcome were examined first in a 2-group structural equation model. The mediational process was then modeled and tested in a parallel process latent growth curve model by relating the prevention program condition, the growth rate factor of the mediator, and the growth rate factor of the outcome.Most prevention studies are based on theories that specify causal variables that have an effect on the outcome, and the prevention programs include the components designed to modify these causal variables to obtain the desired outcome. For example, a drug prevention program based on Social Learning Theory (Bandura, 1977) may include program components to teach adolescents refusal skills and correct their misperception of the prevalence of drug use, aiming to reduce the social environmental influences. A drug prevention program based on the Health Belief Model (Janz & Becker, 1984) may seek to increase adolescents' perception of susceptibility to the negative effects of drugs. If the theory is correct, changing the causal variables, such as social environmental influence for Social Learning Theory and perceived susceptibility for Health Behavior Theory, will prevent drug use.Despite the theoretical basis of prevention programs, most evaluation studies neglect the link between theory and evaluation (Judd & Kenny, 1981;MacKinnon & Dwyer, 1993). Until recently, the success of a prevention trial has been assessed only by the change in the outcome; that is, whether the treatment program reduced the harmful outcome or enhanced the desired outcome. Assessing a prevention trial only by the change in the outcome variable may provide a gross assessment of whether or not a program works, but may fail to identify the underlying mechanisms concerning how the program achieved or failed to achieve its effects. The evaluation of a program should involve more specific investigation by laying out program Requests for reprints should be sent to David P. MacKinnon, Department of Psychology, Arizona State University, Box 871104, Tempe, AZ 85287-1104. davidpm@asu.edu.
NIH Public Access
Author ManuscriptStruct Equ Modeling. Author manuscript; available in PMC 2010 February 12.
NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript components and identifying causal links based on theory (Chen, 1990;Donaldson, Graham, & Hansen, 1994;MacKinnon, 1994).Mediation analysis has been introduced as an appropriate method for theory-driven...