What does "permuted block sizes" mean?

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Context:

2014 Elsevier Ltd All rights reserved.
Cognitive therapy for people with schizophrenia spectrum disorders not taking antipsychotic drugs: a single-blind randomised controlled trial

Summary
Background
Antipsychotic drugs are usually the first line of treatment for schizophrenia; however, many patients refuse or discontinue their pharmacological treatment. We aimed to establish whether cognitive therapy was effective in reducing psychiatric symptoms in people with schizophrenia spectrum disorders who had chosen not to take antipsychotic drugs.
Methods
We did a single-blind randomised controlled trial at two UK centres between Feb 15, 2010, and May 30, 2013. Participants aged 16—65 years with schizophrenia spectrum disorders, who had chosen not to take antipsychotic drugs for psychosis, were randomly assigned (1:1), by a computerised system with permuted block sizes of four or six, to receive cognitive therapy plus treatment as usual, or treatment as usual alone. Randomisation was stratified by study site. Outcome assessors were masked to group allocation. Our primary outcome was total score on the positive and negative syndrome scale (PANSS), which we assessed at baseline, and at months 3, 6, 9, 12, 15, and 18. Analysis was by intention to treat, with an ANCOVA model adjusted for site, age, sex, and baseline symptoms. This study is registered as an International Standard Randomised Controlled Trial, number 29607432.

MOre:
http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(13)62246-1/fulltext

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Type: Question • Score: 4 • Views: 3,587 • Replies: 13

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View best answer, chosen by oristarA

@oristarA,

My God, is this question very hard?

3 Replies

@oristarA,

It's a stats question, ori, and there aren't a lot of statisticians hanging around A2K these days. Permuted blocks is a method of randomization that randomly assigns individuals to a treatment method. In the case of permuted blocks the assignments are based on both a block (method) and a ratio of allocation to the blocks (1:1 this case). Here's a blurb from wiki on permuted block randomization.

Quote:

To balance group sizes in smaller RCTs, some form of "restricted" randomization is recommended.[37] The major types of restricted randomization used in RCTs are:
Permuted-block randomization or blocked randomization: a "block size" and "allocation ratio" (number of subjects in one group versus the other group) are specified, and subjects are allocated randomly within each block.[32] For example, a block size of 6 and an allocation ratio of 2:1 would lead to random assignment of 4 subjects to one group and 2 to the other. This type of randomization can be combined with "stratified randomization", for example by center in a multicenter trial, to "ensure good balance of participant characteristics in each group."[3] A special case of permuted-block randomization is random allocation, in which the entire sample is treated as one block.[32] The major disadvantage of permuted-block randomization is that even if the block sizes are large and randomly varied, the procedure can lead to selection bias.[33] Another disadvantage is that "proper" analysis of data from permuted-block-randomized RCTs requires stratification by blocks.[37] Source

edit: with a ratio of 1:1 this equates to a straight forward randomized block design.

1 Reply

@oristarA,

Quote:

permuted block sizes

I don't know. Maybe that is an American version of the English word "permutated". Or something else, maybe.

I always thought "The Lancet" was a British publication, but that's an American site.

3 Replies

@McTag,

Yes, it is. Meaning, "to change the order of"

per·mute (pər-myo̅o̅t′)
tr.v. per·mut·ed, per·mut·ing, per·mutes
1. To change the order of.
2. Mathematics: To subject to permutation.

0 Replies

@oristarA,

Quote:

My God, is this question very hard?

Ori, you should get used to the fact that you live in a different time zone to most of the rest of us.

And yes, it was quite hard.

0 Replies

@McTag,

McTag wrote:

Quote:
permuted block sizes

I don't know. Maybe that is an American version of the English word "permutated". Or something else, maybe.

I always thought "The Lancet" was a British publication, but that's an American site.

Permute/permuted with that meaning came from late Middle English and has been in English since before the state of Britain existed.

1 Reply

@McTag,

McTag wrote:

I always thought "The Lancet" was a British publication

The Lancet is indeed a UK based medical journal, but it has been owned (along with lancet.com) since 1991 by Elsevier...

Quote:

but that's an American site.

... the Dutch division, based in Amsterdam, of Reed Elsevier, which is the result of the merger in 1992 of Reed International, a British trade book and magazine publisher, and the Dutch science publisher Elsevier.

0 Replies

@oristarA,

oristarA wrote:

My God, is this question very hard?

You keep posting questions about texts from very specialised technical or scientific journals and then getting petulant when nobody answers within 5 minutes.

1 Reply

@JPB,

JPB wrote:

It's a stats question, ori, and there aren't a lot of statisticians hanging around A2K these days. Permuted blocks is a method of randomization that randomly assigns individuals to a treatment method. In the case of permuted blocks the assignments are based on both a block (method) and a ratio of allocation to the blocks (1:1 this case). Here's a blurb from wiki on permuted block randomization.

Quote:
To balance group sizes in smaller RCTs, some form of "restricted" randomization is recommended.[37] The major types of restricted randomization used in RCTs are:
Permuted-block randomization or blocked randomization: a "block size" and "allocation ratio" (number of subjects in one group versus the other group) are specified, and subjects are allocated randomly within each block.[32] For example, a block size of 6 and an allocation ratio of 2:1 would lead to random assignment of 4 subjects to one group and 2 to the other. This type of randomization can be combined with "stratified randomization", for example by center in a multicenter trial, to "ensure good balance of participant characteristics in each group."[3] A special case of permuted-block randomization is random allocation, in which the entire sample is treated as one block.[32] The major disadvantage of permuted-block randomization is that even if the block sizes are large and randomly varied, the procedure can lead to selection bias.[33] Another disadvantage is that "proper" analysis of data from permuted-block-randomized RCTs requires stratification by blocks.[37] Source

edit: with a ratio of 1:1 this equates to a straight forward randomized block design.

Excellent!
Welcome back JPB.

0 Replies

@contrex,

contrex wrote:

oristarA wrote:

My God, is this question very hard?

You keep posting questions about texts from very specialised technical or scientific journals and then getting petulant when nobody answers within 5 minutes.

Five minutes? Impossible. At least 5 hours Contrex.

0 Replies

@contrex,

Quote:

Permute/permuted with that meaning came from late Middle English and has been in English since before the state of Britain existed.

It'd be disappointing if you started getting sniffy with me, matey, because from what I've seen, you need all the friends you can get around here.

This point (and thanks for the information) is interesting to me, because my experience of the word was through training in engineering and mathematics, where one often sees the word "permutation".
I had assumed that the corresponding verb must be "permutate", and I see after checking that this is not so.

One lives and learns, even at my advanced stage.

1 Reply

@McTag,

McTag wrote:

It'd be disappointing if you started getting sniffy with me, matey

That was not my intention. Also I don't post here to get "friends".

1 Reply

@contrex,

McTag wrote:

It'd be disappointing if you started getting sniffy with me, mate
-------------------

Yeah, Contrex, McTag just might stop covering up for your lame responses. Then you'd retaliate and it would be a win win for questioners.

0 Replies

What does "permuted block sizes" mean?

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