What can cause a Difference Between Interview Duration and Net Duration?


SurveyToGo captures the interview duration in 2 different ways, which are fundamentally different. The 2 ways enable you to get a better understanding of what was taking place during the interview. Both durations are available to you as the "Net Duration" and "Duration" fields and In this guide we discuss the difference between them and what it means when the 2 show different values. While in most cases, if you are just interested in knowing how long the interview was, you would look at Net-Duration, for more advanced Quality Control checks you should check both and investigate if there are differences between them. 

* For information on Question Level Duration Capturing please click here

Net Duration

The Net Duration field is the actual time spent interviewing, or in more technical words: "The net amount of time the interview was displaying the question screen as the top window". You can see the value of this duration field in the Interview Review screen under the "Main" tab:


So in the example above 2:56 means the interviewer spent 2 minutes and 56 seconds in front of the interview questions screen. This duration field is captured using an internal mechanism of the app and is not related to the device clock meaning if the interviewer changes the clock mid way through the interview it will NOT have any impact on the value of this field.



The "Duration" field is the more simple calculation of "Submit Time" (end time) minus the "Timestamp" (start time) of the interview (click here to read more about the different time fields captured in SurveyToGo). You can see the value of this duration field in the Interview Review screen under the "Advanced" tab:


So in the example above, 3:00 means the end time of the interview minus the start time was 3:00 minutes. We can quickly verify this by looking at the start time and end times:


This method of duration capturing is dependent on the device system clock. This means that if the clock is changed mid way during the interview or if the interview is stopped and later continued the field will display either non consistent (and sometimes negative) values. 


Differences Between Net-Duration and Duration

As the Net Duration and Duration fields are calculated in a different way, there are sometimes differences in their values. While small differences are usually insignificant, bigger differences (>10 minutes) might mean that the interview needs to be inspected by your Quality Control team.  Next we discuss what these differences can mean. We will take as an example an interview that we expected to take 30-45 minutes and we get the following values:

Net Duration Duration Meaning Recommended Actions
35:00 -05:00 (negative) Negative Duration means that the end time of the interview was earlier than the start time of the interview. Since the Net-Duration is positive we know the actual time spent interviewing was 35 minutes. This would indicate that mid way during the interview the clock of the device moved back either manually or due to a system event. Dooblo logs any clock change action in the interview system log.    We recommend that you check the interview system log to check if the clock was moved backwards manually or due to a system event. In case it was done manually, this would mean that the interviewer possibly tried to modify the clock to somehow optimize his reported work. We would recommend discussing with the interviewer why the clock was changed.
35:00 38:00 In this case the difference between the duration fields is small and is most probably explained by taking photos or switching to an external app for a few moments as the Net Duration would not include this time in the calculation and the Duration field would. No action is needed.
06:00 42:00 When the Net Duration is very short but the Duration field shows our desired duration, it would be a classic case of a suspicious interview that needs further investigation. It is either a case of the interviewer or system event moving the clock of the device ahead in time mid way during the interview OR a case of the interviewer switching to a totally different app (game?) for 38 minutes and only spending 6 minutes actually answering questions. As we expect the interview to take ~30-45 minutes it is not possible that the interview was performed correctly and an investigation is needed.

Check the Interview System Log for manual / system clock changes. If this is not the case, check the interview log for the time/date that appears next to the log entries and try to spot big leaps in time, which would indicate the interviewer switching away from the app and returning. Also check the "Durations" tab in the log that shows you exactly when the interviewer switched away and back to the SurveyToGo app. 

Check if the interview was submitted and re-entered in this case the net duration will not continue to count causing the net duration to be much shorter than the duration

35:00 2d : 40m In this case while the Net Duration shows a valid interviewing time the Duration field shows 2 days worth of interviewing. This  is a classic case of "Stop and continue" of an interview where the interview was stopped for 2 days and later continued. This "stop" time is not counted towards the Net Duration field but is counted in the Duration field. Check in the Interview Review screen that the interview was indeed stopped and continued. You can also verify this in the Interview System Log. If it was stopped and continued and you did not mean for interviewers to do this, you can disable this capability for a survey from the Survey Designer. 



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