The mEMA system allows for a high degree of flexibility in how you make surveys available to your participants. For Momentary surveys there are three levels of daily time windows that can be controlled: The Daily Data Collection Period, the Survey Interval, and the Availability Window.
Daily Data Collection Period:
These are the hours during which Momentary alerts will be scheduled. You control these after you choose the Momentary Schedule type with the Start/End Time fields.
The Daily Data Collection Period in broken up into Intervals within which momentary alerts will be scheduled. An assignment is created at the beginning of each interval. Interval length can be set as minutes or hours. The field labelled "Every" is where you set the interval.
NOTE: We highly recommend having your survey interval be divisible by the total time of your Daily Data Collection Period. This is referred to as an Aligned Interval.
These determine when the survey is available for your participants to complete around the alert. The default is for Momentary Surveys to be available beginning at the time of the alert and until 15 minutes after the alert. You can change this in the participant's "Configure Momentary Parameters" or User Settings window. This is found by pressing the gear icon found on their Survey Assignments page.
The maximum available window configuration is 48 hours prior to alert and 48 hours post, that is, a total availability window of 96 hours.
NOTE: It is recommended to keep the availability window the shortest time which meets the needs of your survey.
An example Momentary survey assignment:
Daily Data Collection Window
Assignment with 120 Minute interval
When you select the Randomize option, the Momentary alert will no longer be scheduled for the beginning of every interval. Instead, it will be scheduled for a random time within the interval. An important consideration is that if the interval is not an Aligned Interval, then the final randomized assignment can occur outside of the Daily Data Collection Period.
Randomized Assignment with 120 Minute interval
Due to the embedded nature of these three time intervals it is important to be aware of how to program each of them so as not to create overlapping windows. There are three possible scenarios.
Aligning the Three Time Periods
1. Aligned Intervals
If your Daily Data Collection Period (Start/End Times) is divisible by the Survey Interval then your alerts will appear as described in the image below. If you do not select "Randomize" then alerts will begin at the beginning of the Daily Data Collection period and continue at the interval set until the end of the Daily Data Collection Period. If you do select 'Randomize" then alerts will occur at a random point within each interval.
2. Non-aligned intervals
If the Start-End time period (below 7.5 hours) is not divisible by the Survey Interval (i.e. the frequency of alerts per minutes/hour) then you have the situation depicted below. That is, when you choose "Randomize" the final alert may fall outside of the start-end times. If this is Ok then leave it, otherwise adjust one of the parameters.
3. Non-aligned with overlapping availability
The availability window (set in the “Configure Momentary Parameters” window) adds another layer of complexity. The window of availability moves with the alert. When there are overlapping windows of availability so that two instances are available when a user enters the app then the most recent survey instance will be presented, even if it has already been completed. Please be aware of this as you program the three time parameters: Start-End Time; Intervals and Availability Windows.
In the images below, you see the same Start-End times with 120 minute Survey Intervals, both Not Randomized and Randomized. The green boxes indicate an Availability Window set to 5 minutes before the alert (blue arrow) to 20 minutes after the alert.