Generate a randomization sequence
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How randomization works
Randomly allocating participants to groups is what lets you attribute differences in outcome to the intervention rather than to who ended up where. Two common schemes:
- Simple randomization: an independent draw for each participant. Unbiased, but in small samples the groups can end up uneven.
- Block randomization: within each block (e.g. of 4) every group appears equally often, so the arms stay balanced throughout recruitment — preferred for small or sequentially enrolled studies.
- Stratify on strong prognostic factors (site, sex, severity) by generating a separate sequence within each stratum.
- Conceal the allocation from whoever enrols participants — generating the sequence is not the same as concealing it.
A reproducible seed lets you regenerate the exact sequence for your audit trail. Record the seed, sample size, groups, and block size in your protocol.
Frequently asked questions
What is block randomization?
The sequence is split into blocks in which each group appears equally often, with the order shuffled inside each block — keeping the arms balanced as you recruit.
Simple or block — which should I use?
Simple is fine for large samples; block guarantees balance and is preferred for small or sequentially recruited studies. Stratify for known prognostic factors.
What does the seed do?
It makes the sequence reproducible — the same inputs and seed always give the same allocation. Leave it blank for a fresh sequence.
Does this conceal allocation?
No — it only generates the sequence. Keep it away from enrolling staff (e.g. sealed numbered envelopes or central randomization).
Does it store anything?
No. The sequence is generated entirely in your browser; nothing is uploaded or saved.
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