I am looking at the snack products that are advertised online over time. I have two variables, snack category (which includes 4 levels - chips, candy, drinks, meals) and time (3 levels - 2010, 2015, 2020). I have the average number of online ads seen by my sample for each year, by food category (i.e., aggregate data). I am wondering if there is a statistical test I could use test the differences between ads viewed by food category over time for aggregate data? Is it possible to use a z test of proportions or chi square?
Thank you.