It bothers me that in some months, the 27th is 3 days from the end of the month, but in some months, the 27th is 4 days from the end. Could this mess up the graph?
The 27th appears in every month, but the time remaining to meet your (possible) quota would be different for different months.
I was originally thinking that the drop on the 31st could be explained by the last day of the month not counting for quotas, so they could be tallied or something. Then I realized that the last day of the month varies, and that it if that was the cause of the massive drop on the 31st, it would have made a bigger impact on the 30th.
I might do an update with some of the suggestions here, including a graph of tickets / days until end of month. [1]
Is there any evidence in regard to the nature of quota-esque incentives? Are the measurement periods monthly vs. say, every two weeks? One would assume that, if quotas exist, they would have some periodicity, but there certainly are other schemes.
The 27th appears in every month, but the time remaining to meet your (possible) quota would be different for different months.