Random selections of a subset of blocks in a survey

wellington
New Member

Posts: 4

Random selections of a subset of blocks in a survey May 11, 2021 8:18:15 GMT

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Post by wellington on May 11, 2021 8:18:15 GMT

Dear colleagues,

I have a small question about the blocks in the questionnaire/survey design. I have created a questionnaire consisting of 14 blocks of stimuli, but I would like each new participant to be presented with a (different) random selection of 7 out of these 14 blocks, otherwise the survey would took them too long to complete. Each block contains sentences spoken by a different speaker (study on prosodic cues to speech act recognition).

I have read the sections on randomization and blocks, but I'm not sure this is possible. As there are 3432 different combinations of 7 numbers out of the [1, 14] interval, this is quite difficult to do manually...

Many thanks in advance for your help!

Nicolas

wellington
New Member

Posts: 4

Random selections of a subset of blocks in a survey May 12, 2021 6:44:36 GMT

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Post by wellington on May 12, 2021 6:44:36 GMT

I thought the following might work, but I don't know how to program it using the right code:

1) A random string of numbers is generated by taking 7 different elements out of [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14], e.g., 3 - 1 - 13 - 10 - 14 - 12 - 5

2) As each number is linked to a block (using a variable?), the participant will be presented with (only) blocks 1, 3, 5, 10, 12, 13, and 14.

As they are 3432 possible combinations of 7 elements out of 14, it is unlikely that 2 participants will see the same sequence of blocks, which is fine.

Do you think it might be possible to do this? Maybe using the code for experiments?

My main obstacle at this stage is: the code for generate random strings of numbers :-).

Thanks again!

matia
Very experienced

Posts: 77

Random selections of a subset of blocks in a survey May 12, 2021 11:06:16 GMT

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Post by matia on May 12, 2021 11:06:16 GMT

Hello,

I've tried something similar.. but didnt have luck. What I tried was to set an array (right at the start in options) to a range from 1-7... and define another array which randomly samples a value from it... (I have tried having all kinds of variables, global, local, arrays...) and then name each block with a number between 1-7 so when I define blockorder I thought that I could use for example $X (beacuse I defined $X under options as a number from 1-7; and I have a block named with a number from 1-7). UNfortunately, this is not possible.

Sorry that I can't be of any help, but maybe I have saved you couple of minutes trying this solution

In case I had more time, I would probably look deeper into arrays, they are very powerful and versatile. I have a hunch that You could solve Your problems using arrays and defining trials under tasks (not under blocks).

Best, Matia

The best time to plan an experiment is after you've done it.

wellington
New Member

Posts: 4

Random selections of a subset of blocks in a survey May 12, 2021 15:23:06 GMT matia likes this

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Post by wellington on May 12, 2021 15:23:06 GMT

Hello Matia,

Thanks a lot for your feedback, it saves me a lot of time indeed!
I think I'll go for plan-B: create say 20 lists based on random combinations of 7 values between 1-14, and recruit 4 participants/list.

Best of luck with your own projects,

Nico