Good morning,

I am trying to create a random number between 0.75 and 1.25 but as a normal distribution (N(1, 0.01) ). Up until now I managed to create the random number between 0.75 and 1.25, however, I am unsure how I can do it as a normal distribution (in other words, I want numbers closer to my original value to be shown more frequently).

This is the code I am using for the random number; however, as far as I understand, the probability that any number between 0.75 and 1.25 shows up is the same and does not follow a normal distribution:

{if(is_empty(wagerandom1),(rand(75,125)/100),wagerandom1)}

I am using an equation question type field.

Thank you in advance and best
Katharina 

Hi,
unfortunately you did not mention if you are allowed to use javascript
and how do you want to use this "random number".

But you may read this
[url] en.m.wikipedia.org/wiki/Box%E2%80%93Muller_transform [/url]
as a background

and use this formula as equation
[url] stackoverflow.com/questions/6241784/gene...istribution-in-excel [/url]

Here's the formula in excel for a normal(0, 1) distribution:

Code:

=SQRT(-2*LN( RAND()))*COS(2 * PI()*RAND())

Then use this formula to scale your normal distribution to mean 10 and standard deviation of 7:
Norm(µ=b, σ=a) = a*Norm(µ=0, σ2=1) + b

This would make the equation in Excel:

Code:

=7* SQRT(-2*LN( RAND()))*COS(2 * PI()*RAND()) + 10

Just try by replacing the Excel function names by LimeSurvey function names.

Joffm

Hi Joffm,

Thank you and sorry about this. Yes, I can use Javascript and I want to use this number in the next question, where I will multiply the wage of a survey respondent by this randomly generated number.

I tried to translate the code in Excel to Javascript, however, I am think I am making mistakes.

I tried the following:

<script type="text/javascript">
    function generateNormalRandom(mean, stdDev) {
        let randomValue = mean + stdDev * (Math.sqrt(-2 * Math.log(Math.random())) * Math.cos(2 * Math.PI * Math.random()));
        return Math.max(0.75, Math.min(1.25, randomValue));
    }

       var randomValue = generateNormalRandom(1, 0.1)

</script>

Thank you very much in advance and best
Katharina

Which type of question do you use to run the script.
Best is a question of type "short text".

And you neither store the result nor do you trigger the script.

So it could be  

That works! Thank you so much!I have one follow-up question (my apologies).I was planning to use the value generated by your code above and multiply it by the wage of a person (let's say 200).I called the question that generates the random number "wagerandom1."In the next question, I tried using: {round(wagerandom1 * 200)}, but the value displayed is always 0.Could you please indicate how I can use the random number in the next question?Apologies for all the questions, and thank you very much in advance!Best,
Katharina

How do you display the survey?
Question by question?
Group by group?

Where is this equation?
On the same page as the script?
This can't work as the script starts on "document.ready", when everything is loaded.

Why don't you just send the lss export?

Joffm 
 

My apologies, here the answers to your questions and attached my lss export:

How do you display the survey? Group by group

Where is this equation? At the beginning of one group
On the same page as the script? Yes, seeing your comment on this, this is probably where my problem starts...

Thank you very much in advance and best!
Katharina

But I think if I move the wagerandom questions to a different question group it works, correct?