The trendline shows the average change in completions. There can be different trendlines based on the averages across days. These lines will typically show a heart beat pattern of upticks after effective communications and down turns and leveling off after the effectiveness dwindles.
In this example, the initial invitations and the day 39 communications (a FedEx package with incentive) showed the greatest effectiveness. As you would expect, the upticks occur a few days after mailings, and the day of for emailing.
