2.1.8 Randomisation

A. Background & Definitions

Randomisation is a process of random assignment of experimental units to treatment conditions:

occurrence of one event should have no influence on the next event (independence principle);
randomisation sequence cannot be based on an easily memorizable and reproducible sequence (randomness principle).

Randomization serves three main purposes:

enables the application of statistical tests based on the central limit theorem;
prevents a potential impact of the selection bias due to differing baseline or confounding characteristics of the subjects;
supports the implementation of other means to reduce the risks of bias (such as blinding).

Randomisation protocol should describe the following:

Type of randomisation (simple / unrestricted, block, stratified, etc.)
Block size (if applicable)
Stratification variables (if applicable)
Tools used for randomisation (including copy of a script if R, SAS or another similar script-based software is used)
Reproducibility of the randomisation protocol such as the seed of random number generator (if applicable)
Reference to the protocol followed (if applicable)
Methods to monitor / detect deviations from the protocol (if any)
If a decision is made not to introduce a proper randomisation protocol, the reasons should be discussed in a declaration justifying the decision to use pseudo-randomisation or simple interspersion methods.

RISK ASSESSMENT

Is pseudo-randomisation used instead of strongly recommended true randomisation?
Is there a risk that randomisation is introduced at allocation of subjects per experimental groups but is not maintained throughout the study conduct, outcome assessment and data analysis?

PLEASE DO NOT FORGET

To consider adding this subject to a training program for new employees or refresher training (if appropriate)
To check whether there are feedback channels installed so that your colleagues can identify, record and report errors and critical incidents related to this subject (if appropriate)

Guidelines on reporting of randomization (in vivo research):

Online tools to support randomisation:

Reading material:

Handbook of Experimental pharmacology chapter on randomization and blinding [2]

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