I'm playing a game in which you can buy and sell items (it's an mmorpg). Now, after certain events, there is a huge drop in the price of certain items (there is a seasonal double experience weekend in which many people grind a lot, causing the market to overflow with certain items). Now, I want to decide which items I could buy right after that double experience weekend to sell a month after. I have the average price of the item per day readily available (I downloaded all the data to my computer) and it can look for example like this:
As you can see, there is a huge drop around the beginning of october after which it will steadily raise again. I only have the data of one of those double experience weekends though... Now, my question is: how can I decide whether an item is a good one to buy in a (semi-)automatic way. Are there any good criteria? I want to calculate a 'score' of an item to decide whether it's a good one or not (let's say that every item is always traded and there is always a sufficient amount of offer and demand). At the moment, I'm looking if a price of an items drops during the days after the double experience weekend and compare it to the price a month later. This still has some errors though, because some items do not respond as fast as other (in their drop). Any theories I should be looking at? Any criteria to investigate? Keep in mine I want to buy DURING the double experience weekend and sell about a month after.
Thanks for your time already!
PS: I also don't know if this is the correct section for my question...