AMC results with empty NULL rows
Rows with too few users show up without a dimension value (NULL) because the aggregation threshold was not reached. This is not a bug.
Symptom
The result file contains rows with metrics where the dimension (for example postal_code) is empty.
Cause
Values of a column only appear if the row covers enough distinct users: at least 2 for the low threshold, at least 100 for medium and high. Below that AMC omits the value. Amazon's example: 95 rows, 4 of them without postal code, 1.5% of purchases.
Fix
- Check what share of the metric sits in NULL rows. If it is small, discard the rows.
- Extend the time window, group days into weeks or hours into 4 to 6 hour windows.
- Roll line items up to campaigns and loosen filters to include more users.
The cause follows the Amazon documentation. Some of the fix steps are our own judgement and do not replace asking Amazon support.