NA while item is mandatory

Hi all,

This question is related to missing values in the dataset that I received from the download. I noticed that there are cases in which participants received an item (based on item criteria) but did not respond, i.e., observation is NA. The strange thing is that the item is mandatory, and follow by another item that did get a response. T

Is there another reason why item responses are marked as NA - besides not marking the item as mandatory, not selecting the item based on item criteria, and participants aborting the survey before the end?

This problem applies to the VAS items in particular.


Hi Teun,

Can you provide an example? One thing comes to my mind is that the survey question is been optional in earlier versions and then made mandatory, and the participant responded to the earlier version of the survey. I can check specifically if I have the user ID, response time, and the question ID which has issues.


Hi Mohammad,

I have an example of an saq item:

survey ID: 4780
ethica ID: 16254
response time: “2019-12-14 11:02:33”

Here, all the other items contain a normal response but item 7_saq is a missing value.

Sorry I cannot find this in the responses. Can you please send the file containing this response to I will follow up there.


1 Like

Sorry Mohammad, I think I gave you the wrong ethica ID… This must be the correct one:

ethica ID: 21256


Hi Teun,

Based on the data we have on our end, I cannot explain why the response to question 7 of survey 4780 is missing for this participant. Everything looks normal, but still the mobile app never sent the response for this question. I suspected this might be an indicator of a bigger issue and checked all the responses, but it seems from all responses provided to the activity 4780 (total of 30420 responses to questions), this is the only instance that is missing.

So my assumption is that this can be because of a data serialization malfunction in the app, where the response could not be properly sent to the server. This is a very unlikely scenario, as if there was any sort of error, we should’ve received the report for that, but we have no error reported from PID#21256. But I could not find any clue to point me to a more probable explanation.

If you have more data, or know about more cases like this, please let me know. That might allow us to find something more useful.