Static block randomization lets you create a balanced and predictable randomization sequence directly in Datacapt, using variable block sizes.
Each block ensures an equal distribution of participants across arms, helping maintain balance while preserving some level of unpredictability.
This method is called static because the full allocation list is generated once before the study starts and follows the predefined block rules throughout.
Before you start
Make sure you have:
The required permission to configure randomization.
Defined the treatment arms (e.g., Treatment A, Treatment B).
Set the desired allocation ratio (e.g., 1:1 or 2:1).
Selected the randomization method (Static, Dynamic, or Import).
Defined the randomization type (Open label or Double blind) and added stratification factors if applicable (e.g., center, gender, age range).
How to configure static block randomization
Step 1 - Go to the Randomization module
Open your study in Datacapt.
Go to the Study settings, open the RTSM tab, and activate Randomization.
Step 2 - Create and configure your randomization
Go to RTSM tab in the study menu
Create your randomization by naming it (the randomization name will be used in the eCRF builder when configuring and the trial supply management for the allocation configuration)
Set up your the arms you want to include in the randomization, give a name and define the allocation ratio between arms (e.g., 1:1, 2:1). Every arms have a unique ID that is automaticcaly generated and that can be used in the eCRF.
Define your randomization method to Block, define your block size (block size are always a multiplication of the number of treatment arms). Block size are define automatically.
Example: a 1:1 ratio with block size 4 will generate 2 allocations per arm in each block.
Randomization type - Chose wether you want to display the arms or not. Describe it.
Define the scope and the stratification:
Per site (independent sequences per site), or
Per stratum (if you use stratification factors).
If stratification is used, Datacapt generates a separate randomization list per stratum.
Step 3 - Add the randomisation action to the eCRF
In the eCRF Builder, open the form where the randomisation action will be placed.
Click Add question and choose # Randomisation.
(Optional) Rename the button label.
Save.
Step 4 - Test the randomisation
In your draft study, generate a new test eCRF.
Click on the Randomise action button.
Confirm the randomisation by selecting "Randomise".
Repeat with multiple test subjects to verify allocation logic
If changes are needed, update the configuration in Settings → Randomisation.
💡Tips :
Test with multiple subjects to ensure the allocation logic is functioning as intended.
If the configuration doesn’t meet your requirements, return to the Randomisation Settings, make the necessary adjustments, and save. Note that this will reset the randomisation to zero, so you’ll need to restart your tests.
Once the randomisation process is validated, avoid making further changes, and proceed to finalize your study for live deployment.
See our Randomisation Glossary for Randomisation button, Randomisation slot, Reset behaviour.
Key points
Live study : No edits after activation: Once static randomization is activated, the list cannot be modified.
If you need to make changes, you must upload a new version.Blinding rules: Blinding levels are handled through user permissions. Users without proper rights will not see the assigned arm.
Already have a randomisation list? You can import it in Datacapt.
👉🏻 Next Step: Run randomisation in a "Live" study