Table 1 SMP quality control checks

Ensured that a few extra phones over the number indicated on initial visit were available and fully charged

Need for extra phones desirable as some children with valid consent may have been absent on initial visit date

Ensured adequate numbers of chargers and adaptors were available and functional

SMPs are shared around the globe from one electrical system to another. In our case the adaptors were necessary to convert to Australian electrical system

Reset the operational frequency of the phones to 900/1800 MHz or as appropriate

900/1800 MHz frequencies were the prevalent frequencies in Australia at study time. This step is very important as the present generation of SMPs is shared amongst various international research centres and operational frequencies do vary from region to region. Most of the SMPs were delivered to us with frequencies set at 1900 MHz. If not changed could suggest a phone fault and can negatively effect participation.

Ensured data collection rate was the same for all phones

Heterogeneous data collection rate can potentially affect exposure allocation of participants and hence introduce bias in a study. In this study data collection rate was uniformly set at 2.5 seconds.

Take the responsibility of Swapping SIM card from participant phone to SMP at beginning and end of use

Participants should not be saddled with this responsibility as problems encountered at this stage could potentially jeopardize participation

Provide participants with a dedicated telephone help number and e-mail address

This service is vital and ensures that participants get prompt help especially with phone and charger faults. Participants may also need to contact investigators at short notice if changing addresses suddenly such as unplanned travel including permanent relocation.