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Abstract:
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Within the NIDA Clinical Trials Network (CTN) studies CTN0018 and CTN0019, two primary measures: drug use and sex under the influence, are count responses with a large amount of zeros. Aim of the CTN studies focused on greater effectiveness for the five session intervention (experimental treatment), relative to the one session intervention (standard treatment). Mediation models assess mechanism through which the interventions work. Moderation models assess modifiers of the magnitude of the intervention effect. Standard approaches to mediation and moderation assumes the mediators and moderators are not confounded by unobserved variables. This assumption is not reasonable for any post randomization variable. Hence, the intervention, mediation, and moderation effects, may not be able to be distinguished from the effects of confounders. Our goal is to present an application of causal inference methods for zero-inflated measures in the assessment of mediation and moderation. The combined CTN data provides sufficient power for this investigation. Comparison between the standard methods and causal method for zero-inflated data will be made.
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