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Your LimeSurvey version: LimeSurvey Cloud, Versión 5.4.3
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Survey theme/template: Demographics
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Hello!!

I need to add an age question as a filter to end the survey. Only participants who are more than 18 can fill the survey. I would like that somebody explain to me in detail how can I do this, since I am newcomer.

Thank you very much in advance! 

Set a quotea with limit 0.
This means you want 0 people with this atrribute to participate.

Now, how do you ask for the age?

1. A list(radio) with age classes
2. a free answer .

1. You can directly enter this code into the quota
2. Insert a question of type equation (eqQuota) with 
{if(QAge<18,1,0)}  "QAge" or however your question is called
Now you set the quota on this question with the answer option "1". These are the respondents younger than 1q8, which have to be sceened out.

Read the manual:
[url] www.limesurvey.org/manual/Survey_quotas/en [/url]

Especially
[url] www.limesurvey.org/manual/Survey_quotas/en#Add_new_quota [/url]

Joffm

Thank you very much Joffm, I really appreciate your kind answer.

Would it be a form to say to the participant that no data was saved before it exit the survey?
Does it exist a form to control that the same participant try to fill the survey again? (i.e returning back with the back browser button).

Super thanks in advance Joffm!!! \o/ \o/ \o/

Does it exist a form to control that the same participant try to fill the survey again?

If the survey is open, anybody who has the general link can take part as often as he wants to.
There is the option to set a cookie to prevent this, but it is only a cookie.

If the survey is token based with the appropiate settings, the respondent can only take part once.

to say to the participant that no data was saved before it exit the survey?

If a respondent is screened out by a quota the data are saved. These data might be important in the analysis of a survey
Example: Even if I prevent people to answer the survey on mobile devices, I may be interested in the percentage of used mobiles.

Only if a respondent leaves the survey using the button "Exit and ..." data are removed.

But these are things you should try by yourself.

Joffm
 

Dear Joffm

Many thanks for your wise answers. I will try to solve these things.