---
title: What happens if I change a stratification variable after randomization has started?
description: Once a patient has been randomized, changing the value of a stratification variable has no impact on the assigned treatment group. Key points to…
---

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# What happens if I change a stratification variable after randomization has started?

Once a patient has been randomized, **changing the value of a stratification variable has no impact** on the assigned treatment group.

# Key points to understand

- The treatment group is assigned **based on the stratification values at the time of randomization**.
- Any change made **after** the randomization does **not** modify the group assignment.
- The patient’s allocation remains locked and is **not recalculated**.

# What happens in the interface?

- If a stratification variable is edited after a patient has been randomized, a **warning message**appears in the right-hand panel of the eCRF:
  
  > “This value was used for randomization. Changing it will not affect the patient’s assigned group but may unbalance study strata.”
- This helps prevent accidental inconsistencies in stratification balance.

# Can I edit stratification variables?

No, most properties of a stratification variable are not editable once you have configured your randomization protocol.

Beware of completely configuring your stratification variables before you configure your randomization.

# Good practice

- Always double-check stratification fields **before** randomizing a patient.
- If you need to correct a mistake, log the reason and notify your data management team or sponsor, depending on your SOPs.

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