Books That Are Part of a Series Are Cash Cows

From a New York Times Inside the Best-Seller List column by Lauren Christensen headlined “From Thriller to Fantasy to Horror, the Genre Series Is the Cash Cow”:

Of the six books that make their debuts on the hardcover fiction list this week — all in their first week on sale — not a single one is a stand-alone novel. Each of these new best sellers is part of a series, its story already long underway for readers before the book even hit shelves.