Hard back, trade paper, and audio book seem to be the options for a new title (I'm assuming ebooks are straightforward to produce once the text is ready for publication). While there may be historic (or policy) reasons for favoring one format over the others, in an ideal world without up-front production costs you would presumably make a new title available in all three formats to give more readers what they want. Since the world isn't ideal, I'm interested in the trade-offs between formats and how you weigh them for a new title. I can understand if you're reluctant to discuss concrete numbers, but perhaps you could compare and contrast formats in relative terms.Well, yes. If there were no up-front production costs, we'd offer every title in hardback, trade paperback, mass market paperback, and large print. But no one has invented a replicator yet, so that's not feasible.
Forget the mass market format (4x6), unless it's a children's book. We don't print enough copies at a time to justify this size for most books. Generally, we go with trade paper (6x9) if we expect fewer to average sales, hard cover if we expect better than average sales. The bigger companies offer audio formats right off; smaller companies only do audio for really good sellers.
You can read about these trade-offs in more depth here.