The JACK Trial: A multi-site cluster randomised trial of an interactive film-based intervention to reduce teenage pregnancy and promote positive sexual health

JACK Trial
Lead investigator
Professor Maria Lohan

Co-Contributors: M Clarke, A Aventin, L McDaid, C Bonell, A Fletcher, J White, H Young, R Hunter, L Maguire, C McDowell, H Reed

The need for gender-sensitive interventions, and especially the need to include teenage boys to reduce rates of teenage pregnancy has been highlighted as a global health need by the World Health Organisation and recommended in systematic reviews. The proposed study will provide a robust evaluation of the effectiveness of a gender-sensitive intervention especially targeting boys. This study follows a NIHR-funded feasibility trial which satisfied all criteria to progress to a full The analysis trial.

The Intervention: ‘If I were Jack’ is an evidence-based, theory-informed, user endorsed intervention which has been collaboratively developed in the UK by a team of researchers, statutory stakeholders, Relationships and Sexuality Education (RSE) experts, pupils and teachers over the past six years. It is a teacher facilitated 4-week RSE Programme, designed to be delivered to pupils aged 14-15 years. Building implementation capacity has been key to its success to-date and, if found to be effective, can be rolled out in schools across the UK through statutory and non-statutory providers.

Aims & objectives
To determine the effectiveness and cost-effectiveness of the 'If I were Jack' intervention in reducing rates of unprotected sex among teenagers under 16 years of age and to better understand the contextual influences on intervention effectiveness through a process evaluation.
Study design

Design and Methods:

Stage one is an intervention refinement deemed necessary as an outcome of 1) Feasibility trial which occurred in Northern Ireland (NI), and 2) Transferability study to test intervention acceptability in the other countries of the UK. Primary refinements are the production of an ‘English version’ of the interactive video drama using English actors to enhance cultural identification in England/Wales, an updated NI/Scotland version, and minor adjustments to classroom materials. These refinements will be assessed against progression (stop/go) criteria before progressing to Stage two.

Stage two involves a cluster RCT in post-primary schools across the UK with embedded process and health economic evaluations. Schools are the unit of randomisation. The primary outcome measure is avoidance of unprotected sex, which is a well-established primary proximate behavioural determinant of teenage pregnancy and represents a commonly measured behavioural outcome in studies examining the impact of RSE on teenage pregnancy [15,17]. We aim to detect a 50% reduction in the incidence of unprotected sex by 15 years of age (from expected rate of 2.8% to 1.4%). To have 80% power to detect a between-group difference of 1.4% at the 12-14 month follow-up, at a 2-sided 5% significance level, assuming an ICC of 0.01 and allowing for attrition, will require 66 schools (33 per arm). Participants across the countries will be pupils with a mean age 14 years at baseline with follow-up data collection 12-14 month post-intervention, prior to potentially leaving school. Secondary outcomes measures are impacts on knowledge, attitudes, skills and intentions to avoid teenage pregnancy, as well as on additional behavioural outcomes of engagement in sexual intercourse, contraception use, and sexually transmitted infections. The analysis will be on an intention to treat basis.

Expected outcomes: A robust evaluation of a gender-sensitive intervention.


Further information & publications

For further information about the JACK Trial, please contact Dr Honor Young on or 02922 510085

Start date
January 2017
End date
December 2020