Why is my book jumping categories?

[T.L. Haddix]

I know this has been discussed here, as I've seen the thread titles, but have never paid much attention to them. Perhaps I should have.

Two of my books, Secrets and UTMS, are climbing high these days. And they're also jumping from branch to branch. Secrets is supposed to be classified (and shows up when I checked my settings on KDP) as Suspense and Romantic Suspense. It's showing up in Mystery, Mystery and Thrillers, and Literature and Fiction.

UTMS should be the same categories. Instead, it's showing up in Suspense (whoohoo!) and Contemporary Fiction. HUH?

Is this just the Amazon system being wonky or what?  I'm not freaked out about it - sales are going. But it's just a little odd.

[Terrence OBrien]

Someone posted an Amazon email recently saying the KDP categories are BISAC. (I don't know what that means.) However, Amazon uses a different set of categories and fits the BISAC category chosen in KDP into the Amazon categories.

I have seen three different sets of categories in Amazon. Kindle store on the web has one breakdown, paper has another, and the hand-held Kindle unit shows a third. They all have been changing over the last few months. I suspect they are moving to one standard set.

[T.L. Haddix]

But shouldn't the books stay in the categories that are picked when the books are published?

[Terrence OBrien]

This is list management. If the lists are being reduced, stuff has to move. If they stay the same size, some categories are dropped, and some added, stuff has to move. If they think books in category XYZ will sell more in category ABC, stuff has to move. If they want to balance the numbers in XYZ and ABC, stuff has to move.

It's the same problem faced with any list, and any hierarchy. They tend to grow like weeds, and overall effectiveness can be reduced. It's rarely a comment on any specific member of the list.