Gutschoven K et al. 2005 [35]

Flanders, Belgium,

15 Schools. Data collected from Leuven Study on Media and Adolescent Health (SOMAH)

Cross-sectional

Random sampling of schools. All students were selected from 1st & 4th year (Data derived from the media and adolescent health project)

1380 boys

1166 girls

ANOVA with post hoc Tukey’s test

Henderson M et al. 2008 [36]

Tayside and Lothian, Scotland,

24 Scottish schools. Data collected in 1998 and 1999 at the first follow-up of the SHARE trial.

Longitudinal study

Not stated

5092 boys and girls

Two level logistic regression model

Henewinkel R et al.2007 [37]

Schleswig Holstein, Germany, 27 Schools in Oct-Nov 2005

Cross-sectional

Random sampling of schools.

2861 boys

2717 girls

Chi square test, Lowess (locally weighted scatter plots), Logistic regression

Henrikson L et al. 2008 [38]

California USA,

135 High schools in 2005-06

Cross-sectional

Random sampling of schools

384 boys and girls

Multiple regression for complex sampling design

Hublet A et al. 2006 [39]

9 European countries, 2 UK counties and Canada, Number and types of schools not specified. Study from 1990-2002

Cross-sectional

Cluster sampling of schools & classes

36, 767 boys

38,978 girls

Logistic regression

Kokkevi A et al. 2006 [40]

5 European countries (Bulgaria, Croatia Greece, Romania, Slovenia) and UK. High schools in 1999

Cross-sectional

Two stage sampling stratified by school type 16445 boys and girls

Survey logistic regression

Kristjansson AL et al. 2009 [41]

Iceland, Secondary schools, in March 2006.

Cross sectional

9th-10th grade students of all Icelandic secondary schools

3612 boys

3620 girls

Pearson’s correlation & logistic regression

Leatherdale ST et al. 2005 [42]

Ontario, Canada, 57 Elementary schools. Data collection time not mentioned.

Cross-sectional

Not stated

2758 8th grade boys and girls

4286 6th or 7th grade boys and girls

Multilevel logistic regression

Leatherdale ST et al. 2007 [43]

Ontario, Canada,

29 Secondary schools, in 2000-2001

Cross-sectional

Not stated

511 9 boys and girls grades 9 - 12

Multilevel logistic regression

Lee LK et al. 2005 [44]

Malaysia 7 districts, Sermban, Port Dickson, Kualapilah, Jempaltampin& Remban, 14 Schools, from June 2001-August 2002

Cross-sectional

Multistage stratified random sampling, 6 schools from urban, 8 schools from rural

2 classes per school

2088 boys

2411 girls

Chi-squared test & CI

Lovato CY et al. 2007 [45]

British Columbia, Monitabo, Newfoundland, Ontario and Quebec

81 Secondary schools. Data collection year not mentioned.

Cross-sectional

Random sampling of schools

22,318 boys and girls

Grades 10 - 11

Linear regression analysis, t-test

Mathur C et al. 2008 [46]

Delhi (n = 16) and Chennai (n = 16), India, 32 Public & private school in 2004

Cross–sectional

Convenience sampling 11,642 boys & girls

Mixed effects regression model