The study ID has three components:
- 2 digit study number
- 4 digit site code
- 4 digit randomisation number
Study IDs are stored as character variables but a decimal point is included between the site code and randomisation to allow the ID to be more easily converted to a numberical variable and manuipulated. The randomisation number is assigned after randomisation and is sequential at each site, allowing sites to monitor their recruitment. The study number is essential to ensure that records and sample between studies remain separate.
The following site codes have been used in previous Australasian multicentre trials and are recommended for continuity:
Randomisation in multiple pregnancy
To deal with unit of analysis issues, there are two common solutions:
- Add a suffix where 0 is mother; infants are coded 1, 2 and 3 according to birth order in multiple pregnancy or 5 for singleton. A surviving twin would be coded as 1.
- Assign a separate "randomisation number" to the infant(s) at birth, e.g., start at 5000 or