Equal number of participants in random groups

[Katerina M.]

Hi everyone!

My apologies if this has been asked before, but I'm trying to find a way to assign the same number of participants to each random group in my run. I have three different between-subjects conditions as different survey sheets, and I have used shuffle to randomise assignment to each one. However, I would like to have a balanced number of responses across all conditions. I think that the block.random function from the psych package would be useful for that, but I'm not sure how to add it as a calculate-type item to my survey sheets. 

Any help would be greatly appreciated! :) 

Thanks a lot,

Katerina

[Ruben Arslan]

Hi Katerina,

you can put the following in a calculate field's value column:

set.seed(100)

planned_sample_size <- 300

groups <- 3

psych::block.random(planned_sample_size, groups)[.formr$nr_of_participants, 2]

Put in some random seed and choose the number of participants that you

plan to recruit. 

You will have to manually end the study when you have reached your planned

sample size, or put something in your run that deals with the case when you run

out of numbers.

Best,

Ruben

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[Katerina M.]

Hi Ruben,

Thank you for your answer! Just to make sure, do I add this code to a separate sheet which I would put before my conditions, or to each of my condition sheets? Also, in [.formr$nr_of_participants, 2], what is 2 referring to?

Many thanks again for your help!

Best wishes,

Katerina

On Monday, April 1, 2019 at 7:27:22 AM UTC+1, Ruben Arslan wrote:

Hi Katerina,

you can put the following in a calculate field's value column:

set.seed(100)

planned_sample_size <- 300

groups <- 3

psych::block.random(planned_sample_size, groups)[.formr$nr_of_participants, 2]

Put in some random seed and choose the number of participants that you

plan to recruit. 

You will have to manually end the study when you have reached your planned

sample size, or put something in your run that deals with the case when you run

out of numbers.

Best,

Ruben

On Sun, Mar 31, 2019 at 3:36 AM Katerina M. <epi...@gmail.com> wrote:

Hi everyone!

My apologies if this has been asked before, but I'm trying to find a way to assign the same number of participants to each random group in my run. I have three different between-subjects conditions as different survey sheets, and I have used shuffle to randomise assignment to each one. However, I would like to have a balanced number of responses across all conditions. I think that the block.random function from the psych package would be useful for that, but I'm not sure how to add it as a calculate-type item to my survey sheets. 

Any help would be greatly appreciated! :) 

Thanks a lot,

Katerina

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[Katerina M.]

Hi, 

Sorry for the repost but I'd really appreciate an answer here (I'm really new to this!). 

Thanks!

Katerina

[Ruben Arslan]

Hi Katerina,

while testing, you cannot break anything—when in doubt, try it out. 
I don't know anything about your study except what you told me, so I don't know what's best. Probably separate sheet from the way you asked.

The 2 refers to the second column from the output of block random. You can run the code in your local R to understand the parts better.

Best,

Ruben

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