I have two stores. each store sends a notification when they make a sale. The notification specifies how many of a specific item were sold.
Some days no notifications, other days several. For example store A send 45 notifications of total 78 items for January 2019, compared to 40 notifications of total 68 items for January 2020.
I receive a monthly report of the notifications. I created a column with cumulative sale of the item along the year.
I am comparing the cumulative sales of the item over the years 2019 and 2020. I find a clear decrease of cumulative sales during 2020 because of covid. Now I would like to compare the two stores regarding the COVID-related decrease in sales in 2020 ( relative to 2019). For example STORE A showed 11% decrease in total sales of the item for 2020, relative to 2019, while store B had only 6% drop.
I would like a statistical test to compare the decrease. the problem is that the number of notifications are different between month and years for the same store, and between stores for the same time period.
How do I test whether covid impacted the two store differently?
