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

Overview

SurveyToGo captures interview duration in two different ways, each measuring a different aspect of the interview process.

These duration values are available as the Net Duration and Duration fields. Understanding the difference between them can provide valuable insights into how an interview was conducted.

This guide explains what each duration represents and why the two values may differ.

In most cases, if you simply need to know how long an interview took to complete, Net Duration is the value you should use. However, for more advanced quality control analyses, it is recommended to review both Net Duration and Duration and investigate any significant differences between them, as they may indicate interruptions or unusual interview behavior.

 

Net Duration

The Net Duration field represents the actual time spent conducting the interview. More specifically, it measures the total amount of time during which the interview question screens were actively displayed as the top window on the device.

Unlike the overall interview duration, Net Duration excludes periods when the interviewer navigated away from the interview screen, minimized the application, or switched to another app. As a result, it provides a more accurate measure of the time actively devoted to interviewing the respondent.

You can view the Net Duration value 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.

 

Duration

The "Duration" field is the more simple calculation of "Submit Time" (end time) minus the "Timestamp" (start time) of the interview. 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.