OK I inserted the string you suggested into the equation question. Where should the survey IDs now be entered? And what do I enter in the end-url?

 

Hi,
first: There are HTML tags in your equation "randnum" So this will not work. Remove them.
You seem to have pasted it. Never do this!

YAour end-url is fine, if the result of "randnum" is a valid surveyID.
At the moment you get only "0", "1", "2".

Here I show two options.
The first I mentioned before:
Create your surveys with these six surveyIDs like
111111
111112
111113
...
Now you can distribute your respondents randomly with an equation like
{if(is_empty(randnum),sum(111110,rand(1,6)),randnum)}
and your end-url is like this
2. Nested IF
Create a random number (1-6) the usual way
{if(is_empty(randnum2),rand(1,6),randnum2)}

In a next equation (eqSID) select the surveyID (linefeeds for easy reading, don't copy/paste)
and the end-url is like
You can put this second equation directly into the end-url field, as described here
[url] manual.limesurvey.org/URL_fields/en#Expressions [/url]
but I do not recommend it.

 

In the real survey the equations will be hidden, of course.

Joffm

Thank you very much,
I am in the process of constructing the last surveys but I think I have succeeded! I have one last question: how can I make sure that each respondent is randomly assigned to a survey and that each survey is completed by an equal number of participants?
Probably the number should not be random but each entry should be assigned to survey x, the next one to survey y.

how can I make sure that each respondent is randomly assigned to a survey

You see the IF-statement. Here you see that ANYBODY is assigned to one of the surveys.
  

and that each survey is completed by an equal number of participants?

This is something you can't.
A random number is a random number. But the percentual difference from an equal distribution will be smaller with a high number of participants.
Roll a dice and count, you will see.
  

 should not be random but each entry should be assigned to survey x, the next one to survey y.

Instead of a random number you could use the SAVEDID and the same MODULO calculation as before.
{1+SAVEDID-x*floor(SAVEDID/x)}
with x=number of groups.

But it is not better than a random number.
There are always respondents who do not complete a survey.

One more workaround is:
Watch the distribution and if one group is filled you switch the relevance equation.
Before After group 3 is filled but group 5 is a bit low
Or there is a plugin "getStatInSurvey" by DenisChenu.
[url] gitlab.com/SondagesPro/ExportAndStats/getStatInSurvey [/url]
Here you have a "leastfilled" option.

You see, there are many options.
But these are basics which you can think about yourself.

Joffm

Answers given by Joffm are good. You can also check survey.tuni.fi/help/limit-registrations.html to get an idea about statCountIf()-function, but I think you won't need it.

However, if the survey for some group is faster and easier than for other group, then it is of course possible that you will not get at all similar number of responses for all groups.