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Comparing drug policies: An assessment of the validity and reliability of the global drug policy index
David Bewley-Taylor 
,
Matthew Wall ,
Jack Tudor,
Alison Ritter
,
Matthew Wall ,
Jack Tudor,
Alison Ritter
International Journal of Drug Policy, Volume: 143, Start page: 104908
Swansea University Authors:
David Bewley-Taylor , Matthew Wall , Jack Tudor
-
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© 2025 The Authors. This is an open access article distributed under the terms of the Creative Commons CC-BY license.
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DOI (Published version): 10.1016/j.drugpo.2025.104908
Abstract
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 meth...
| Published in: | International Journal of Drug Policy |
|---|---|
| ISSN: | 0955-3959 1873-4758 |
| Published: |
Elsevier BV
2025
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| Online Access: |
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| URI: | https://cronfa.swan.ac.uk/Record/cronfa70059 |
| first_indexed |
2025-07-30T12:16:06Z |
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| last_indexed |
2025-08-01T10:29:43Z |
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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. 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. 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. 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.</abstract><type>Journal Article</type><journal>International Journal of Drug Policy</journal><volume>143</volume><journalNumber/><paginationStart>104908</paginationStart><paginationEnd/><publisher>Elsevier BV</publisher><placeOfPublication/><isbnPrint/><isbnElectronic/><issnPrint>0955-3959</issnPrint><issnElectronic>1873-4758</issnElectronic><keywords>Global drug policy index; Comparative policy analysis; Un system common position on drug-related matters</keywords><publishedDay>1</publishedDay><publishedMonth>9</publishedMonth><publishedYear>2025</publishedYear><publishedDate>2025-09-01</publishedDate><doi>10.1016/j.drugpo.2025.104908</doi><url/><notes/><college>COLLEGE NANME</college><department>Social Sciences School</department><CollegeCode>COLLEGE CODE</CollegeCode><DepartmentCode>SOSS</DepartmentCode><institution>Swansea University</institution><apcterm>Another institution paid the OA fee</apcterm><funders>Wall and Tudor are affiliate members of the Global Drug Policy Observatory at Swansea University, and in this capacity received research support funding from the Robert Carr Fund. 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2025-07-30T13:18:22.0577076 v2 70059 2025-07-30 Comparing drug policies: An assessment of the validity and reliability of the global drug policy index 0807b03501c47902946df41da4ddf2a4 0000-0003-1724-4223 David Bewley-Taylor David Bewley-Taylor true false 22914658d586a5759d4d4b945ea140bd 0000-0001-8265-4910 Matthew Wall Matthew Wall true false df9894ac4288a616edc2bae7d573c89a Jack Tudor Jack Tudor true false 2025-07-30 SOSS 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. 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. 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. 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. Journal Article International Journal of Drug Policy 143 104908 Elsevier BV 0955-3959 1873-4758 Global drug policy index; Comparative policy analysis; Un system common position on drug-related matters 1 9 2025 2025-09-01 10.1016/j.drugpo.2025.104908 COLLEGE NANME Social Sciences School COLLEGE CODE SOSS Swansea University Another institution paid the OA fee Wall and Tudor are affiliate members of the Global Drug Policy Observatory at Swansea University, and in this capacity received research support funding from the Robert Carr Fund. Tudor is in receipt of a Leverhulme postdoctoral fellowship, while Wall’s ongoing research is funded as a Co-Director of the Wales Institute of Social and Economic Research and Data (Funding reference: UKRI264: People, Places and the Public Sphere). Alison Ritter receives funding from the National Health and Medical Research Council (NHMRC), Australia (GNT2016695). 2025-07-30T13:18:22.0577076 2025-07-30T13:02:38.5682664 Faculty of Humanities and Social Sciences School of Social Sciences - Politics, Philosophy and International Relations David Bewley-Taylor 0000-0003-1724-4223 1 Matthew Wall 0000-0001-8265-4910 2 Jack Tudor 3 Alison Ritter 4 70059__34872__758693cd82e64d71b78090d5b06b324e.pdf 70059.VOR.pdf 2025-07-30T13:10:48.0130226 Output 3483237 application/pdf Version of Record true © 2025 The Authors. This is an open access article distributed under the terms of the Creative Commons CC-BY license. true eng http://creativecommons.org/licenses/by/4.0/ |
| title |
Comparing drug policies: An assessment of the validity and reliability of the global drug policy index |
| spellingShingle |
Comparing drug policies: An assessment of the validity and reliability of the global drug policy index David Bewley-Taylor Matthew Wall Jack Tudor |
| title_short |
Comparing drug policies: An assessment of the validity and reliability of the global drug policy index |
| title_full |
Comparing drug policies: An assessment of the validity and reliability of the global drug policy index |
| title_fullStr |
Comparing drug policies: An assessment of the validity and reliability of the global drug policy index |
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Comparing drug policies: An assessment of the validity and reliability of the global drug policy index |
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Comparing drug policies: An assessment of the validity and reliability of the global drug policy index |
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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. 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. 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. 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. |
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2025-09-01T05:29:51Z |
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