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 |