In contrast to qualitative surveys, e.g. interviews, it is quite difficult to avoid multiple participation in online surveys. Especially when the survey will be released publicly and thereby will be accessisble for anybody in the internet.
Allow multiple participation
In some surveys it does make sense to allow multiple participations. E.g. if an interviewer collects and enters the answers manually and does not publish the survey link, but still wants to benefit from the automatic evaluation.
Reduce multiple participation
Generally it is hard to completely avoid, that certain participants answer your survey multiple times. Basically our survey tool is able to save the IP address and the respective session-ID of each participant and to set cookies. Therefore if somebody uses another computer and opens the survey link again, the system does not know, that this person has already participated. Nevertheless there are various options to protect oneself from unrequested multiple participation resp. to reduce them.
Reduce multiple participation by locking the participants browser session ID and setting a cookie (recommended and standard default)
The browser of a participant communicates an unique session-ID to our system, which will be recognised by a repeated try to anwer the questionnaire. Thereby the access will be denied. Furthermore our system sets cookies, which allow us to recognise a participant, even though the session-ID could have been changed.
Advantages:
Avoids the majority of simple tries to answer the survey again. Additionally this method is very reliable, as the sytem barely identifies a multiple participation mistakenly.
Disadvantages:
This protection can be bypassed very easily, if somebody knows how the session-IDs and cookies work. E.g. by using another browser (the session-ID changes and cookies have not been set yet) or computer.
Lock the participants IP address
Hereby the IP address of each participant will be stored and locked for any further participations.
Advantages:
Safe protection against multiple participation and tougher to envade.
Disadvantages:
Lots of companies externally use the same IP address for all their employees. This means, if one person of a company has already took part in the survey, all other employees cannot participate anymore, because the IP address of this company is locked. Thus this method involves the risk that some people are unjustly excluded. Additionally this protection can be avoided by using another computer (with different IP address).
The use of individual survey links
To guarantee the exclusion of multiple participations by 100% you have to use individual survey links. This method requires, that each recipient has to be contacted personally, as each person receives an own, individualised link. You will find more information about this method in the following link: Create individual survey links. Another option would be to use our internal email distributor.
Advantages:
The securest method to avoid multiple participation. Furthermore you are able to track your participants. Thereby you are able to assign the collected responses to the particular participants (provided that you do not conduct an anonymous survey) and to send targeted reminder emails.
Disadvantages:
The most time-consuming method, as each participant needs to be contacted personally (e.g. with a mass mailing programm). But with our email distribution no problem!