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Additional Information

Competing Interests

The authors declare they have no competing interests.

Author Contributions

Robert Patton conceived and designed the experiments, performed the experiments, analyzed the data, wrote the paper.

John Strang wrote the paper.

Catherine Birtles performed the experiments, wrote the paper.

Mike Crawford wrote the paper.

Data Deposition

The following information was supplied regarding the deposition of related data:



Funding was provided by the charity Action on Addiction. The funder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

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