DAX Functions for Participant Days in Study

This document outlines two DAX measures designed to calculate the number of days a participant has been in a study, based on their registration date and today's date. The first measure calculates the total days for all participants, while the second measure calculates days based on selected participants through slicers or date ranges.

1. Measure for All Participants

Description

This measure computes the total number of days that all participants have been enrolled in the study by subtracting the registration date from the current date.

Code

Total Days in Study = 
VAR TodayDate = TODAY()  -- Get today's date
RETURN
    SUMX( 
        Participants,  -- Assume 'Participants' is the table containing participant data
        DATEDIFF(Participants[RegistrationDate], TodayDate, DAY)  -- Calculate the difference in days
    )

Explanation

• TODAY(): Retrieves the current date.
• SUMX(): Iterates over each participant to calculate the number of days since their registration.
• DATEDIFF(): Computes the difference in days between the registration date and today.

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2. Measure for Selected Participants

Description

This measure calculates the number of days participants have been in the study based on the current filter context (slicer selections or date ranges).

Code

Selected Days in Study = 
VAR TodayDate = TODAY()  -- Get today's date
RETURN
    SUMX( 
        FILTER(Participants, NOT(ISBLANK(Participants[RegistrationDate]))),  -- Ensure RegistrationDate is not blank
        DATEDIFF(Participants[RegistrationDate], TodayDate, DAY)  -- Calculate the difference in days
    )

Explanation

• FILTER(): Ensures the measure processes only participants with a valid (non-blank) registration date.
• SUMX(): Like previously, it sums up the days calculated for each filtered participant.

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Input Validation

Both measures handle potential issues by verifying that registration dates are valid and not blank. The use of NOT(ISBLANK(...)) provides an extra layer of validation for the second measure.

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Usage Example

Assuming you have a table called Participants structured as follows:

• Total Days in Study will return the cumulative days for all participants based on their registration dates.
• Selected Days in Study will return days only for those participants selected through slicers applied in Power BI, allowing for dynamic reporting.

These measures can be added to cards or any visual where tracking participant study duration is necessary, facilitating comprehensive analysis and insights on participant engagement over time.

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Conclusion

These DAX measures encapsulate best practices for calculating the duration of participant involvement in studies, providing both a holistic and a context-sensitive view of engagement. By leveraging functions like DATEDIFF, SUMX, and FILTER, the code remains efficient and scalable for various data contexts.

For further enhancement of your DAX skills, consider exploring courses on the Enterprise DNA Platform!