About the Authors
- Matthew C. Farrelly
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* E-mail: mcf@rti.org
Affiliation Research Triangle Institute (RTI) International, Research Triangle Park, North Carolina, United States of America
- James M. Nonnemaker
- Kimberly A. Watson
Competing Interests
The authors have declared that no competing interests exist.
Author Contributions
Analyzed the data: KAW. Wrote the paper: MCF JMN KAW.