Sample size
RECRUITMENT
Statistics from QLD and NSW in Australia in 2022 suggest there is a large population of P1 licence holders aged 18–20 years to sample from: 32,151 young drivers in QLD [To detect a 1.5% absolute reduction in the incidence of young drivers having a police-reported crash of any type during the 24-week intervention and post-intervention periods, from 3% in the control group to 1.5% in the intervention group (or 0.5 relative risk), using a two-sided type I error of 5% and a power of 80%, a total of 3,068 participants are required. Allowing for a 15% non-response rate due to drivers who may choose to withdraw from the study, turn off their phones, or delete the smartphone app, 1,805 participants per arm, or a total of 3,610 participants, will be recruited to participate in the trial.To achieve adequate participant enrolment and reach the target sample size, recruitment strategies will be carried out in partnership with government stakeholders. The transport departments from the three states of Western Australia, Queensland, and New South Wales will assist with advertising the trial via several media channels, including social media, associated websites, and advertising boards in licencing centres.