I would like to invite participants to repeat a part of the survey after 6 and 12 months. Is it possible with Limesurvey to reinvite participants for a second and third measure, and what would I need to do to hide a part of the survey in the second and third measure and to enable within subject comparisons? Thanks in advance!

Iterate survey - www.limesurvey.org/manual/Iterate_survey

and what would I need to do to hide a part of the survey in the second and third measure

Hide them by relevance equation. You can do this while a survey is active.

Joffm

Thank you Tony! Follow up question: does this allow me to automatically reinvite only those participants that replied to the first measure?

Thans you for your reply Joffm, glad to read that this is indeed possible! Where in the menu can I find the option to ‘hide by relevance equation’? (working in a Dutch version of Limesurvey)

Follow up question: does this allow me to automatically reinvite only those participants that replied to the first measure?

No, that is not a built-in option. A couple of (untested) workarounds...

1)
- Export the "completed" tokens
- Delete all tokens
- Import "completed" tokens CSV
- Continue with the iterate-survey process

2)
- Export all data
- Export the "completed" tokens
- In the resulting CSV file, edit the "invited", "reminded", "remindercount", "completed" and "usesleft" columns
- Deactivate the survey (this will remove all data and tokens)
- Activate the survey
- Import the "completed" tokens CSV
- Modify the email templates
- Send invitations as you did for the first survey

Either you hide each question
www.limesurvey.org/manual/Question_type_...y#Relevance_equation
(this is the part of the manual referring to arrays, but it is the same for each question type)

or - much better - you hide the entire groups
Here you see where you enter the relevance equation
www.limesurvey.org/manual/Question_group...estion_group_actions

By the way: You want to compare the results of your three waves.
So you need a variable in your dataset which contains the wave.
In my opinion the best is (and to enter the relevance equation easily) is:

At the start of the survey create a question of type equation (hidden), call it "wave" and enter just this (in the first wave.)
{1}
Now all questions resp. groups which are not displayed in the following waves get the relevance equation wave==1

In the second and third wave you only have to change this equation to {2} and {3}.

Now you have a variable ("wave") in your dataset and the questions/groups are not displayed in the following waves.

Joffm