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.


John Toumbourou
(Deakin University)
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Dr Jennifer A. Bailey
(University of Washington)
Jess Heerde
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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.

Data access

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.

Time period


Original sample size

AUS: 2884, USA: 2885 (Total 5,769)









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) and Deakin University (2007-136, 2018-096). This project only (Specific consent)


Wave Year / Period 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)
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)

Key references

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

View publications list

Primary institution

Collaborating institutions

Major funding sources


Cohort Representative

Professor John Toumbourou (Australian arm)

+61 3 5227 8278

Dr Jennifer A. Bailey (US arm)

+1 206-616-9115


Centre for Adolescent Health,
Level 2 East, The Royal Children’s Hospital,
Parkville, VIC 3052

Social Development Research Group School of Social Work,
University of Washington, Seattle

Study website