Because most adolescents abstain from HED, variables for HED usually have excessive zeros exhibiting overdispersion. Consequently, modeling adolescent HED use is a challenging task. One solution is to use zero-inflated Poisson (ZIP) modeling that allows the researcher to simultaneously estimate the zero (probability of abstaining from HED) and count (level of HED) components of the outcome variable (Greene, 1994; Lambert, 1992).
