Fun with numbers and graphs - part 1

Recently, I've had the opportunity to combine my day job as a software engineer with my night job as an author.  I used my programming skills--with some help from Robert A., a graphics expert--to analyze how well my I WISH series was selling after I paid for a promotion from Bookbub (a company that provides e-book promos for authors.)

As you'll see in the graph below, the pertinent dates to remember are:

• January / February 2016: the sales for I Wish and Wishing for You were languishing
• March 9: the Bookbub promotion ran with I Wish discounted to $0.99
• March 14: I returned I Wish to its regular price of $2.99 

So my primary interest was to discover: what effect did the promotion have on my book sales? 

To begin, I collected sales data from Amazon, B&N, Apple, and several other e-tailers. Then I ran some analysis on the data and produced a set of graphs to visualize what happened.

In the graph below, I've plotted unit sales for six weeks before the promotion as well as six weeks after.

1. The first red arrow on the graph marks the day that the promotion ran.
2. The second red arrow highlights when the book returned to regular price.

On promo day, there is an expected spike in unit sales. Over the five days following the promotion, the unit sales decline, but they are still much higher than before the promo. But the interesting--and unexpected--result is that the higher sales of I Wish continued after I set the price back to normal.

But there is an even happier conclusion we can see in the above graph. Unit sales through May 1st never dip to the pre-promotion levels--a result that has remained true until this day.

This second graph represents the effect that the I WISH promo had on its sequel, Wishing for You. Note that the sequel remained at regular price throughout the promotion period.

The first red arrow shows promo day. There is a mild spike that lasts for several days before going into a slight decline.

Approximately two weeks after the promotion, we see a new spike! As an author, I hope that the second spike means they've read book 1 and enjoyed it enough to buy the sequel.

After the second spike, sales remain somewhat sporadic, but still higher than before the promotion. Just as I experienced with I Wish, I can confirm that the unit sales of the sequel remain higher even 4 months after promo day!

 
Moral of these graphs: I have been delighted with the results of this promotion. The Bookbub ad created an expected spike in unit sales during the promotion period. Since then, unit sales for Book 1 as well as its sequel have been consistently higher than before the promotion. I am a satisfied Bookbub customer!