By David Bewley-Taylor,  Matthew Wall, Jack Tudor, and Alison Ritter 

Background

The Global Drug Policy Index (GDPI) is an instrument that attempts to comparatively evaluate national drug policies at a global scale. This paper assesses the validity and reliability of this new Index, speaking to the wider question of whether such a comparative evaluation can be achieved in a methodologically robust manner.

Method

We review the validity of the Index through analysis of the conceptual logic of the GDPI. Construct validity is assessed using Cronbach’s alpha statistics alongside exploratory factor analysis (EFA). The reliability of the Index is assessed using uncertainty analysis where we systematically analyse how Index rankings vary across simulations with randomly perturbed weighting schemes. In addition, we explore the reliability of experts’ assessment of policy implementation, reporting on a common vignette undertaken by all country-expert evaluators.

Results

The analysis of conceptual validity is a reproduction of the logic supporting the contention that the project’s underpinning normative document (a report produced by the UN system coordination Task Team on the Implementation of the UN System Common Position on drug-related matters) represents a solid starting point of what will be a sustained, iterative research process to develop a valid conceptual and operational basis for comparative evaluation of national drug policies. The empirical analysis of construct validity reveals that operationalising the Common Position creates a set of variables with a coherent multidimensional structure that is amenable to aggregation into an overall index. While the performance of states under simulations of different weighting schemes was highly consistent, country expert evaluation in developing state codes on policy implementation can be inconsistent, even when they are provided with a common description designed to capture variance on their rating scale. Cronbach’s alpha indicates that the variables encompassed by the GDPI measure a coherent construct, while EFA results provide support for three of the a priori dimensions used in the creation of the Index.

Conclusions

We conclude that the GDPI project demonstrates that robust comparative evaluation of drug policy at a global scale is possible. However, we also reveal that this project will necessarily be subject to continuous refinement – especially when it comes to standardising expert country evaluations. We outline practical challenges and suggestions for future work in this direction.

International Journal of Drug Policy Volume 143, September 2025

By Dave Bewley-Taylor, Tom Blickman, and Martin Jelsma 

Cannabis has long been a substance drawing much attention within the international drug control regime, a system currently based upon the 1961 Single Convention on Narcotic Drugs. Today the regime landscape is changing. Faced with particular challenges and democratic decisions, a number of jurisdictions are moving beyond merely tolerant approaches to the possession of cannabis for personal use to legally regulating markets for the drug. In November 2012 voters within the U.S. states of Colorado and Washington passed ballot initiatives to tax and regulate cannabis cultivation, distribution and consumption for non-medical purposes. Just over a year later, Uruguay legislated state regulation of the entire chain of the domestic cannabis market for medical, industrial and recreational use. These policy shifts go well beyond the permitted prohibitive boundaries of the UN drug control conventions. They represent a break with an historical trajectory founded on dubious science and political imperatives. And they have thrown the global regime into a state of crisis, as this report will argue. This publication is a joint effort of the Transnational Institute in Amsterdam and the Global Drug Policy Observatory at Swansea University. Research has been going on in various stages for about two years, and interim results were presented at the Seventh Annual Conference of the International Society for the Study of Drug Policy at the Universidad de los Andes, in Bogotá, in May 2013 and further discussed in an expert seminar on cannabis regulation in October 2013 in Amsterdam. Many academics, government officials and experts from NGOs and international agencies have provided useful comments on earlier drafts, but needless to say the end result is the sole responsibility of the authors. This final report will be first presented at the 57th session of the UN Commission on Narcotic Drugs (CND) in Vienna, 13-21 March 2014  

Amsterdam: Transnational Institute / Global Drug Policy Observatory, 
March 2014, 88p.