are the total number of hits a variable value was either defined or (for conversion variables) persisted. The metric is in essence the sum of page views and page events.
Occurrences higher than Instances: This outcome is expected for conversion variables, as occurrences also includes the number of times the variable was defined (instances).
Instances higher than Occurrences: This outcome is not possible in reporting, as all instances are recorded as occurrences as well.
Instances equal to Occurrences: This outcome is most common for traffic variables, as by nature they do not persist beyond the image request.