Clinical Trial Randomization Tool

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For clinical trials, educational purposes, or just for your own interest.
Uses MTI randomization to generate the allocation sequence.
Default values are provided below. You may adjust these as you require or prefer.
When you click “Request Confirmation Email,” your request will be sent to a server. You will receive an email when your download is ready (typically in a few minutes).
For more detailed instructions, you may view the Tool Instructions page.

Basic Trial Info

A simple trial design is used by default. For more complex trials, change the trial settings below to customize arms and/or stratification.

Number of Trial Arms: 2

Arm:

Ratio:

Arm 1

Arm 1

Arm 1 Allocation Ratio

Arm 2

Arm 2 Allocation Ratio

Stratify Trial: False

Variable 1

Category Names

Based on the number of categories for your 1 stratification variables, your trial will have 1 strata. For each stratum, you will receive one worksheet containing 1,000 assignments.

Algorithm Parameters

The following parameters should work well for most trials, but can be further customized.

Randomization Method: Asymptotic Maximal

Maximum Tolerated Imbalance (MTI): 3

Select a method to use for randomization. All methods shown use MTI randomization and are suitable for use. For more information about these different methods, consult the Learn About Randomization page.

Randomization Method

Asymptotic Maximal

The most under-assigned arms are always favored by a balance-forcing probability that varies based on the current degree of imbalance.
Big Stick

Neither arm is favored until the MTI threshold is reached — each arm's probability of assignment is always 0%, 50%, or 100%, based on the current imbalance. The Big Stick method is a special case of Chen's procedure where the balance-forcing probability is 50%.

This method is supported only for two-arm trials with an arm allocation ratio of 1:1.
Chen's Procedure

The under-assigned arm is always favored by a preset balance-forcing probability, e.g., 60%. Chen's procedure is a generalized version of Big Stick where the balance-forcing probability can be greater than 50%.

This method is supported only for two-arm trials with an arm allocation ratio of 1:1.

Maximum Tolerated Imbalance (MTI)

At any point in the randomization process, for any stratification group, no trial arm will be assigned more than this many participants than any other arm.

The MTI can be any integer between twice the largest allocation ratio and 20.

Balance-Forcing Probability

At any point when the arms are imbalanced, this is the percent probability that the next enrollment goes to the arm that currently has fewer enrollments. When both arms have equal number of enrollments, the probability is 50% to each arm. If assignment to the larger arm would violate the MTI, the probability is 100% and the next enrollment goes to the smaller arm.

You may enter any value between 50.0% and 99.9%, but the higher the value, the less random the procedure. We default to 60.0%.

Contact Info

The Clinical Trial Randomization Tool is a web application developed by the National Cancer Institute (NCI) and the National Institutes of Health (NIH) to help researchers generate randomization sequences for their clinical trials.

A study statistician should be consulted in conjunction with the design and implementation of your randomization scheme to ensure it is appropriate for your clinical trial. NCI and NIH are not responsible for how any randomization sequence is used in a clinical setting.

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