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Clinical Trial Randomization Tool

For clinical trials, educational purposes, or just for your own interest.

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.

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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.

Trial Name

A short identifier for your trial. When your randomized assignments are downloaded, the files will be labeled with this name.

Participant Count

Max: 10,000. For unstratified trials, this will be the total number of participants in the trial. For stratified trials, this will be the number of participants per stratum.

Customize trial arms
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The number of arms in this trial.Number of Trial Arms:
2

One or more values in this section are invalid. Please adjust them before submitting.

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.

Stratum names

Your results will use the following names for each stratum's sequence worksheet. Due to length restrictions in Microsoft Excel, category names may be truncated.

One or more values in this section are invalid. Please adjust them before submitting.

Confirm reset

Are you sure you want to erase your stratification parameters?

Algorithm Parameters

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

Customize MTI method
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Randomization Method:
Asymptotic Maximal

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.Maximum Tolerated Imbalance (MTI):
3

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.Balance-Forcing Probability:
60.0

One or more values in this section are invalid. Please adjust them before submitting.

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, but the degree of bias 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 either 50% or 100%.

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%. 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.

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%.

One or more values in this section are invalid. Please adjust them before submitting.

Confirm reset

Are you sure you want to erase your MTI method parameters?

Note: The default value for the MTI is 3, which is disallowed for your current set of allocation ratios. The MTI will be reset to its lowest valid value of 3 instead.

Contact Info

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We will email you at this address when your results are ready!

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