This is a pretty straight-forward question but the answer, I can't seem to find anywhere. I've come across all sorts of research about online shopping habits but for the past week I have spent a couple hours each day trying to find a study on the average percentage of people that check out an item, bookmark it and purchase it later because let's say they're waiting for payday or alike. The reason I'm asking is due to ad campaigns I'm running. It seems a lot of my ad clicks do not lead directly to sales. The thing is that if I stop running ads, my sales crash the following month. From this I can guess my own range but there's also normal sales fluctuations to take into account so I figure my "range" is probably fairly inaccurate. In normal circumstances Google Analytics would help me figure this out but the nature of my business makes it so that a lot of sales come via word of mouth. What this means is that I have sales coming from people visiting directly which is how visits from bookmarks would appear in GA so it's hard to separate the two. Although my ads don't tend to directly lead to sales it's becoming obvious over the past half a year that a decent portion must be bookmarking and returning. Basically I'm just trying to get an average percentage range for this sort of behavior to aid in planning my ad spend, if any data even exists.