Really helpful charts and breakdown of the data. Some of it seems blatantly obvious--of course people with more books published are going to earn more money! Of course those who spend more on editing and covers are going to see a greater ROI!--but honestly, when you are looking at dismal sale numbers and asking yourself if it's worth keeping on with this next book, if it's worth getting that editor, etc, it can be hard to see things so clearly. Because all you see is you pouring yourself into the work and nothing coming out of it. So having that chart is really helpful, to be able to say, "yes, it is worth continuing, it is worth making everything as professional as possible, eventually perseverance will have its reward."
Keep in mind, those numbers are averages. For every average, there are highs and lows that can be far removed from the average. For instance, I spend more than double the editing cost shown in stage five, more than $2000 per book. Including audio recording costs, I'll spend in excess of $7000 before a book is released. And I've a long way to go to reach the average number of books published for stage five, my 24th will be out in two weeks. I'm no longer in Select, so my income from KU is now less than 10% of gross and falling by the day. If they were to carry it further and create a Stage 6, you'd probably find that authors at that stage spend less time writing. At he most, I'll write 20 hours a week.
But if Stage 5 were $10,000 to $25,000, they'd have to create a new stage for me and many others. I'd be really interested to see the numbers for those who are earning $500,000 a year.