My previous post about BookBub concerned the type of ads book bub accepts. In this post I will look at performance, focusing primarily on discounted books in preference to free downloads. Free downloads might have such goals as generating reviews for the book, establishing a fan base for the author, or encouraging readers of the free book to purchase subsequent works in the series. A heavily discounted book might have any of these goals as well, but may also expect to repay advertising costs through increased book sales. BookBub of course cannot guarantee that ads will generate sufficient sales to earn back the costs, but from the analysis below, I think they typically do. I do not herewith endeavor to contradict BookBub’s published sales predictions, but rather to expand upon them.
See the footnote  for a few words about the limitations of my methods. Because my estimates of sales are speculative, I only present these estimates to compare factors such as book price, book rating, number of reviews, day of week, ad’s position on the page, etc. So do not consider them for any other purpose than entertainment. In addition to the method limitations mentioned in the footnote, sometimes authors run ads in other media on the same day as the BookBub ad. For example, Amazon has Countdown Deals and Free Promotions that might coincide with a BookBub ad. While this is rare, it could make a particular BookBub ad appear to be much more effective than it would have been alone.
Fifteen books – one day:
Let’s first look at a typical day. Here we see book rank for the first fifteen books on the Latest Deals list for 8/3/2014.
Note: Rank is plotted on a logarithmic scale since ranks here vary from #1 to #119,553. On a linear scale most of the data on the graph would just be clutter at the bottom.
The time axis runs from 04:00 Pacific time on 8/3 through midnight on 8/4. The Latest Deals page typically updates between 05:00 and 06:00 Pacific. Although the ad will disappear by 06:00 on the following day, I continue to track the books’ ranks for the rest of that day.
The free books often change rank before the paid books. This may be because Amazon updates free and paid ranks on a different schedule. Some books respond soon after the ad appears, but most take many hours, usually not until around noon Pacific time. This delay could be due to Amazon’s schedule for updating ranks. The early response of some books may occur because the book is already being promoted elsewhere and is experiencing sales/downloads by the time the BookBub ad goes live.