What format should the kit code be?
The kit code can be any format – it can be a simple number (1, 2, 3...), a box/pack number (2000/21) or an alphanumeric code (AF3, TY8). Some issues to bear in mind when choosing a format are:
- Each code must be unique. Do not repeat codes or use the same code at different sites.
- If using a number format, kits should not be allocated in a way that leaks information inadvertently about the treatment allocation. For instance if you used the list shown in the table below and codes were allocated in the order 1, 5, 2, 3 you might guess that the second patient was given a different treatment because codes 2 to 4 were skipped. To prevent this Sealed Envelope systems randomise the order kit codes are allocated within kit blocks. This means the codes jump around whilst still being allocated in approximately ascending order.
| Kit code | Treatment |
| 1 | Active |
| 2 | Active |
| 3 | Active |
| 4 | Active |
| 5 | Placebo |
| 6 | Placebo |
Code list with sequential codes