See https://doi.org/10.1111/j.1360-0443.2007.02041.x for the original paper, and [this link](https://htmlpreview.github.io/?https://github.com/academy-of-behavior-change/determinants-of-ecstasy-use-and-harm-reduction-strategies/blob/master/scripts/determinants-of-ecstasy-use-and-harm-reduction-practices.html) for GitHub's HTML preview of this study's R Markdown document.