The International Youth Development Study (IYDS) is a long-term study that looks at the development of healthy and problem behaviours among young people in the state of Victoria, Australia  and the state of Washington, United States. IYDS is one of the first studies designed to examine whether or not differences in Australian and American school policies affect youth development. The study began in 2002. The original sample included approximately 1000 students at each of three year levels in both Victoria and Washington, giving a total of nearly 6000 participants. The study continues to follow-up participants into young adulthood.

For more information on the Australian arm of IYDS, please refer to the Australian study cohort page.


Study name  International Youth Development Study
Study abbreviation  IYDS
Current principal investigator/s  Dr Jennifer A. Bailey (University of Washington)
Current project manager  Dr Jennifer A. Bailey
Cohort representative (study contact)  Dr Jennifer A. Bailey
Postal address Social Development Research Group School of Social Work, University of Washington, Seattle
Phone  +1 206-616-9115
Primary Institution  Social Development Research Group, University of Washington
Collaborating Institution/s  Centre for Adolescent Health, Murdoch Childrens Research Institute, Deakin University
Major funding sources  NHMRC; ARC; NIAAA; NIDA
Study website 
Key reference McMorris, B.J., Hemphill, S.A., Toumbourou, J.W., Catalano, R.F. and Patton, G.C. (2007). Prevalence of substance use and delinquent behavior in adolescents from Victoria, Australia and Washington State, United States. Health Education and Behavior, 34: 634-650. doi: 10.1177/1090198106286272
Are data available outside study team? Data are available according to study protocols, namely: approval of proposal by Principal Investigators; Data Sharing Collaboration Agreement read and agreed to by all parties, Fair Use Agreement signed by applicant and Principal Investigators
Study focus  Risk and protective factors, as well as healthy and problem behaviours in young people including substance use, delinquency, violence, risky sex, depression and self-harm
Sampling frame In 2002, a two-stage cluster sample design was used to recruit students in both states (Victoria, Australia and Washington State, USA). In the first stage, schools were selected at random, based on a probability proportional to grade-level size from a stratified sampling frame of all schools in Victoria (government, Catholic and independent) and Washington (public, private and alternative). At Stage 2, single intact classes from each school for the selected grade level (Grade 5 (Youngest), 7 (Middle) or 9 (Oldest)) were chosen at random; in a few cases, 2 classes from different year levels were randomly chosen at a school.
Year commenced  2002
Commencement sample AUS: 2884
USA: 2885
(Total 5,769)
Intergenerational? No
Imaging No 
Linkage No 
Biosamples? No 
Ethics approvals or requirements?

The IYDS has ethics approval through the following Human Research Ethics Committees – Royal Children’s Hospital (20086), University of Melbourne (060045X), Deakin University (2007-136, 2018-096) and University of Washington (study #00000680). This project only (Specific consent).


Wave Year Age (mean, range) Eligible sample
1 2002  AUS: 13, 9.8 – 16.5 (Y) (M) (O)
USA: 13.1, 9.7 – 17.2 (Y) (M) (O)
2884 (Y) (M) (O)
2885 (Y) (M) (O)
2 2003   AUS: 14, 11 – 17.4 (Y) (M) (O)
USA: 14.1, 10.8 – 18.4 (Y) (M) (O)
2884 (Y) (M) (O)
2885 (Y) (M) (O)
3 2004   AUS: 14, 11.9 – 16.5 (Y) (M)
USA: 15.1, 14 – 18.6 (M)
1909 (Y) (M)
961 (M)
4 2006   AUS: 15.2, 14.1 – 16.5 (Y)  927 (Y)
5 2007   AUS: 16, 15 – 17.4 (Y)  927 (Y)
6 2008   AUS: 17, 16.1 – 18.6 (Y)  926 (Y)
N/A 2009   AUS: 19 – 22 (M) (O)  Tracking and locating survey only
F1 (Follow-up 1) 2010   AUS: 21, 17.9 – 24.6 (Y) (M) (O)  2872 (Y) (M) (O)
F2 (Follow-up 2) 2012 AUS: 23, 20 – 26.9 (Y) (M) (O) 2871 (Y) (M) (O)
F3 (Follow-up 3) 2014 AUS: 25, 22 – 28.9 (Y) (M) (O)
USA: 25, 24 – 26 (M)
2870 (Y) (M) (O)
955 (M)
F4 (Follow-up 4) 2018 USA: 29, 28 – 30 (M) 783 (M)
F4 (Follow-up 4) 2020 USA: 31, 30 – 31 (M) 783 (M)