If you do not need to combine, then you do not need a variable. You can just start the survey2 from the end-URL of survey1. There is one caveat: once the URL of survey2 is known to others, people from outside could fill in survey2, also. I have never encountered that, but it is a possibility. Keep the start-URL of survey2 hidden as much as you can.

If your survey is among students or other people that may want to find out how things work, you might want to have survey2 check if the referring URL is that of survey1.

Tammo

And if you really want everything to be as anonymous as can be: in survey2 switch off everything that is shown on the tab "Notification & data management".

Even then a clever person could find out via the server logs what happened, but that is something more obscure. Maybe you can even switch off server logging. But I am not sure about that.

Thanks very much Tammo and sorry for my very late response - I can see that I got the autoemail from the forum, but I guess I simply forgot to look here (or maybe I thought it was an old reply?) Anyway, the only question that remains is this one:

"Are passthrough field values stored somewhere in the system?"

Hope someone can answer this little question so I don't have to start a new thread just for that.

passthrough field values ar NOT stored.

But you can easily use another system for the same functionnality

manual.limesurvey.org/URL_fields#Prefill...using_GET_parameters is an example.

Thank you. I actually don't need to store the value - in fact I need to make sure it isn't stored in any log etc. Good that it isn't stored.