Block randomization random permuted blocks

This is a method to ensure that after the entry of every x patients into the trial, the number of patients on each treatment will be equal; 'x' is referred to as the block size.

ID no.

TRT

Patient initials

Hospital

1001

3

1002

2

1003

3

1004

3

1005

1

1006

3

1007

3

1008

1

1009

2

1010

2

1011

3

1012

1

1013

1

1014

3

1015

2

1016

3

1017

3

1018

3

For example, in a trial of two treatments with a block size of four, we can ensure that of every four patients, two will receive treatment A and two will receive treatment B. The random element comes from considering all the possible arrangements of, in this example, two As and two Bs within a set of four, and then randomly choosing the order in which the sets are used to form a randomization list. Again using the example above, there are six possible permutations of two treatments (A and B) within a block of four:

To implement blocked randomization, allocate a digit (0-9) to each block, and use random numbers to choose the order of the blocks to be used in the randomization schedule.

For example, given the random number sequence 1843712 ...

^ AABB (ignore 8) BBAA ABBA (ignore 7) AABB ABAB

0 0

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