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What is Randomization


Random Allocation Software


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About the Author







An important aspect of any trial which should be clearly stated in the final report is the method used to assign treatments (or other interventions) to participants. Random assignment has been used for more than 50 years and is the preferred method of assignment. Randomization eliminates the source of bias in treatments assignment; facilitates blinding the type of treatments to the investigator, participants, and evaluators; and finally randomization permits the use of probability theory to express the likelihood of chance as a source for the difference between outcomes.

In a clinical trial (and perhaps most other multigroup researches) participant should be assigned to comparison groups on the basis of a chance (random) process which should be unpredictable. In the final report of the trial authors should specify the method of sequence generation, i.e. whether they used computer generated random list or the used random number table, etc. In addition if any restriction in the process of randomization has been used it should be clearly stated.

Randomization may have no restriction. i.e. a single sequence of random assignment. This type of randomization is known as simple randomization. When the sample size is relatively large simple randomization is expected to produce equal sized treatment groups. Restricted randomization is used to control the randomization to achieve balance between groups is size (or other characteristics). Different types of restricted randomization are as follows:

  1. Blocking: Blocking is used to ensure close balance of the numbers in each group at any time during the study. After every block the number of participants in each group would be equal. Of course blocking tends to reduce the unpredictability of randomization. Therefore it is recommended to use random block sizes when using block randomization.
  2. Stratification: Stratification ensures that the numbers of participants receiving each intervention are closely balanced within each stratum. Stratified randomization is achieved by performing a separate randomization procedure within each of two or more subsets of participants
  3. Minimization: Minimization is not a method of randomization. Indeed it is the only non-random method which is an acceptable alternative to randomization. Minimization ensures balance between intervention groups for several patient factors. Randomization lists are not set up in advance. The first patient is truly randomly allocated; for each subsequent patient, the treatment allocation is identified, which minimizes the imbalance between groups at that time.



Random Allocation Software


Random allocation software has been produce to support the first type of randomization, i.e. block randomization. This software produces as its output a sequence of allocation based on the selected type of blocking. Below is the description of this software.

Random Allocation Software is a Windows software which install in the same way as ordinary windows software (i.e. running setup.exe and following on screen instructions). After installing and running the software the main window will appear which is as follow.


Number of groups Sample Size Groups Save settings on exit



Steps to generate a random sequence


1. Select the number of groups (2 - 16)

2. Enter the name of each group

3. Enter the sample size

4.Select 'Generate' from the 'Sequence menu'




Setting the block options

1. Only one block: This produces a single sequence of random assignment (Simple Randomization)

2. Equal size: If you select this option, you should specify the size of each block. The output will be block randomization with block of the same size. The specified block size must be devisable by the number of groups

Final sample size in block randomization may be greater than the specified sample size. Block sizes must be devisable by the number of groups.

3. Random sizes of: The output will be block randomization with block sizes varying randomly among the specified block sizes.

4. Random block size: The program randomly select the number and size of each block


After last step Option Window will appear. you can accept the current settings for code and bock options or change them. Finally click OK to generate the random sequence. Depending on the type of selected output the generated sequence will go into a file, a window, or into the clipboard.



Setting the code options

Each participant in the trial will be given a unique code. This code can be numeric, alpha, or alphanumeric. In addition, codes can be sequential (e.g. 001, 002, 003, 004 ...) or random order. You can specify the code length from 3 to 10 character.



File menu


1. Load Settings


Opens the file open dialogue box to select a setting file (*.stg). Setting file contain different options of randomization (number and names of groups,  sample size, code and block options and output type


2. Save Settings


Opens the save as dialogue box to save the current settings in a file (*.stg). Setting file contain different options of randomization (number and names of groups,  sample size, code and block options and output type


View menu


1. Random file


Opens the file open dialogue box to select an output file to open. Any kind of html file can be opened


2. Options


Opens the Options Window which is used to set the block and code options.


Sequence menu


1. Output


You can select to output the generated sequence to file, window, or windows system clipboard.


2. Generate


Generate the random sequence based on the selected options. Before generating the sequence, the Option Window will appear to accept or change the code and block options.



Number of groups

Select the number of groups in your trial. Between 2 to 16 groups can be selected. When changing the number of groups the table of group names resizes to match the new number.


Sample Size

Enter the sample size here prior to produce random sequence. Sample size must be devisable by the number of groups.


Select a group to edit its name and then enter the name of selected group in the textbox.

Save settings on exit

Check this option to save the setting on exit. The next time you have the same setting with respect to number and names of groups, sample size, blocking and code options and output type.

About the Author

Random Allocation Software has been developed by M. Saghaei, MD., Department of Anesthesia, Isfahan University of Medical Sciences, Isfahan, Iran. Email:

Usage of this program is free for instructional, educational and research purposes, provided that the reference be made in the report to this program for the generation of random list. This program can not be used for commercial purposes


Random Allocation Software

Version 1.0, May 2004