APPENDIX

Study Sample Details

GermanyIcelandItalyPolandThe NetherlandsScotland
SettingPublic schools, 4 school types: Gymnasium Gemeinschaftsschule, Regionalschule, HauptschulePublic schoolsPublic schools, second class of secondary school and first class of high schoolPublic schools, 1 school type (Gymnasium)Public schools, 4 different school types: VMBO, HAVO, Atheneum, GymnasiumMainstream (state-funded) schools
LocationsSchleswig-Holstein, GermanySchools from each region (north, south, east, west) of Iceland in addition to the capital area (Reykjavík)Piedmont region, ItalyWielkopolska regionGelderland, Limburg, BrabantCentral belt of Scotland
District of Kiel, Flensburg, Schleswig-Flensburg, and Rendsburg-EckernfördeSchools with head office in Turin and Novara provinces
Time of baseline assessmentNovember–December 2009January–February 2010March–June 2010April–June 2010December 2009–June 2010January–March 2010
Time of follow-up assessmentFebruary–March 2011January–February 2011March–May 2011January–April 2011February–May 2011January–February 2011
Eligibility criteria for schoolsLocationNumber of participating pupils >100Location in Turin and Novara provincesLocation in Wielkopolska regionNo special pedagogic education centerLocation in either Midlothian or East Dumbartonshire
Number of classes >8No special pedagogic education centerNo current participation in other studies of the BSI, Radboud UniversityNo special education
No special pedagogic education centerNo private education
No other studies of IFT-Nord
No. of schools potentially eligible104Not known578253Not known14
No. of schools invited602331253437
Invitation criteria for schoolsRandomConvenience samplingConvenience samplingAll eligible schoolsRandomSelected based on proportion of free school meals
No. of schools that agreed (baseline)2120263557
No. of schools that agreed (follow-up)2120263357
Eligibility criteria for pupilsActive (“opt-in”) parental consentPassive (“opt-out”) parental consentActive or passive parental consentActive (“opt-in”) parental consentPassive parental consentPassive (“opt-out”) parental consent
Presence on the day of assessment or, if absent, willing to complete a questionnaire and return by postPupil’s presence on the day of assessmentWillingness to participate or, if absent, willing to complete a questionnaire and return by postPresence on the day of assessmentPresence on the day of assessmentPresence on the day of assessment or, if absent, willing to complete a questionnaire and return by post
Willing to participateWilling to participateWilling to participateWilling to participateWilling to participate
No. of pupils examined for eligibility354427982953507817063189
No. confirmed eligible275426642668410514232937
Reasons for nonparticipationNo parental consent (n = 515), absence (n = 264), refusal (n = 11)No parental consent (n = 19), absence (n = 102), refusal (n = 13)No parental consent (n = 100), absence (n = 175), refusal (n = 10)No parental consent (n = 396), absence (n = 527), refusal (n = 50)No parental consent (n = 18), absence (n = 265), refusal (n = 0)No parental consent (n = 11), absence (n = 226), refusal (n = 15)
No. participating at baseline275426642668410514232937
No. analyzed at baseline275426642668410514232937
Response rate at baseline (%)789590818392
Mean age at baseline (y)12.713.113.614.213.813.0
No. participated at follow-up264525942404369816763012
No. matched233621682272314812152503
Reasons for nonmatchAbsence at baselineAbsence at baselineAbsence at baselineAbsence at baselineAbsence at baselineAbsence at baseline
Absence at follow-upAbsence at follow-upAbsence at follow-upAbsence at follow-upAbsence at follow-upAbsence at follow-up
Incorrect codeIncorrect codeIncorrect codeIncorrect codeIncorrect codeIncorrect code
No. of baseline pupils lost to follow-up388496396957208434
Matching rate (%)84.881.485.276.784.480.0
  • BSI, Behavioral Science Institute.