Randomly assign participants to differnet question groups

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1 year 6 months ago #179936 by Ellaisa
Hello everyone,

I tried to randomly assign participants to differnet question groups.
I have created 2 different szenarios within 2 different questiongroups. Some people should see szenario 1 and the other szenario 2.
Therefore I created a question group (that is always hidden) including in one question the randomization with: if(is_empty(randnumber.NAOK), rand(1, 2), randnumber.NAOK) - question type is equation

Now I have created another question group, that is my first szenario. In the relevance euqation I have added: randnumber == "1"

Afterwards my questions for this szenario follow.

I have done the same with szenario number 2, only changed: randnumber == "2"


I tought that this should lead to a 50/50 randomization. Now I have started a pretest and I mostly offers szenario 1 (85% of participants).

Can anyone tell me what I have done wrong or could do better?

Thanks a lot!

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1 year 6 months ago #179937 by tpartner
What is your sample size? The larger the sample size, the closer you will get to 50/50.

You might also try:

if(is_empty(randnumber.NAOK), rand(1, 100), randnumber.NAOK)

And then use relevance:

intval(randnumber) < 51
intval(randnumber) > 50

Cheers,
Tony Partner

Solutions, code and workarounds presented in these forums are given without any warranty, implied or otherwise.
Official LimeSurvey Partner - partnersurveys.com

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1 year 6 months ago #179938 by Ellaisa
Thanks!
Until now I have 40 completed questionnaires.
I was just wondering, as the first 10 were only scenario 1, afterwards 2x scenario 2 appeared and then it went on with scenario one.

I will try your solution!
Can you see any mistake in the way I did it? Or should it work out with a bigger sample size?
I need at least 100 participants

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1 year 6 months ago #179940 by Joffm
Hi, Ellaisa

everything you did was fine.
But as always:
If you throw a coin 10 times, you won't expect it to be a 5/5 distribution.
If you throw it 100 times, you won't expect a 50/50 distributiion, but will be nearer to a 50%/50%.

I just tested:
40 times with randnumber=rand(1,2): 19 times 1, 21 times 2
40 times with randnumber=rand(1,100): 18 times 1-50, 22 times 51-100


To be able to finetune a distribution survey, I prefer the following:
1. create your random number : r1=rand(1,100)
2. The relevance of your 2 scenarios is: r1<51, resp. r1>50.

If you see that the distribution gets unbalanced, just change the relevance equation (e.g. too much "2") like
scenario 1: r1<31
scenario 2: r1>30

or even (you only need "2")
scenario 1: r1==0
scenario 2: r1>0

You can do this, even if the survey is activated.

Best regards
Joffm


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1 year 2 months ago #185207 by nannancy
Hey, you can try

{SAVEDID - floor(SAVEDID / 2) * 2 + 1}

in the equation field of the hidden question.

Best
Xinyuan

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1 year 2 months ago #185210 by Joffm
Of course you can use the SAVEDID.

But it is not sufficient, because the SAVEDID is incremented each time a survey is started.
So "not completed" surveys have a SAVEDID as well.
So, if by chance each second respondent does not complete the survey only odd SAVEDIDs are completed and you have all respondents in one group.

Therefore I'd prefer the random number, but checking the distribution from time to time.

Joffm


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1 year 2 months ago #185216 by DenisChenu
A good idea of puglin :woohoo:

Assistance on LimeSurvey forum and LimeSurvey core development are on my free time.
I'm not a LimeSurvey GmbH member, professional service on demand , plugin development . I don't answer to private message.

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2 months 2 weeks ago #199674 by AnnaSSSA
Hi!
I'm working on a randomization procedure following the steps suggested into the message #179936.
When I did that 1 week ago, all was working.
Now, I have opened the survey preview and nothing is working... the hidden group question (used to randomize) is working, because it report a random number, but the group questions to show do not appear.
Which kind of error could be occurred?
What I'm sure to have done was to modify the title and description of the group question (used to randomize) and the text of the questions to show. But they are not part of the equetions used for randomizing.
Please, help me, I don't know what think about!
thanks!

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2 months 2 weeks ago #199676 by Joffm
Hi,

Which kind of error could be occurred?

It's like "The car doesn't start. What's wrong?"

Without even seeing your survey and your settings, what to say?

So, please, send a LSS export of your survey.

Joffm


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2 months 2 weeks ago - 2 months 2 weeks ago #199682 by AnnaSSSA
Of course...
These are in order the first three survey groups

Respondents' profile
XXX
the group for randomizing
XXX

the first questions' group to show randomly. I avoid to send the other 9.
XXX

thanks!
Attachments:
Last edit: 2 months 2 weeks ago by AnnaSSSA.

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2 months 2 weeks ago #199684 by Joffm
Hi,

we always ask for a lss export.

lsq and lsg exports are language sensitive.
And we have to create a survey first - hopefully with the same base language as the exports - to be able to import the group or question.

Joffm


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2 months 2 weeks ago #199719 by AnnaSSSA
Hi Joffm,
I think I have solved the mystery. My problem was the preview option that I had activated (full questionnaire). When I shifted to the group' view everything was visible.

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2 months 2 weeks ago #199756 by Joffm
Hi, Anna,

therefore it is important to send lss exports.
Here the survey settings are included.

If we only import a question or a group our settings are taken, and we may talk for years without finding the issue.

Joffm


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