Should You Write Your Non-fiction Book?

I recently had an individual contact me to ask questions about the content of one of my non-fiction books (I only write non-fiction). In the course of corresponding the individual asked if I was considering writing a book about a topic within the broad scope of my field of expertise. Unfortunately, the topic is not one I consider myself to be an expert in. For example, I might be a doctor who practices internal medicine. I would not be the specialist you would see for knee replacement surgery.

The individual asserted correctly this topic was one that would have broad appeal to the market I write for. This made me stop and think about the possibility of writing the requested book. I thought about books I had written and had not sold well. I also thought about the titles I have written that have sold well and are continuing to do so. In the process I came up with a set of guidelines to use in determining future titles I will invest the time and energy to write, publish and market.

First, is there a market for the book? Not do I want to write the book, is there a demand, need or market for the book? My two biggest duds in terms of sales have no demand. There was not a market for the book. The time, effort, energy and money invested were wasted. My successful titles sell because there is a need for the information. Some of my books are not big sellers but they sell a few copies each month. Over time, those small monthly sales add up. Those books were worth writing as well.

The second question I arrived at is am I an expert in the topic? If I were to write a book on a topic in my field that I was not qualified to be considered an expert, would this impact the sales of the books I am a legitimate expert in. The risk to my credibility is not worth risk to me.

Do I have the time and skill to effectively market the new book? Can I develop an effective plan? As I publish more books, I find I spend more time on marketing efforts and less time on producing new books. More books that sell means more income for the business. Selling books requires time and effort. Time and effort are required to write more books. You can see the situation develops into a bit of a catch-22.

Some other questions include:

Do I have the ability to reach my target audience?

If I am not an expert, am I willing to invest the time to develop the expertise?

Will the book be profitable?

How will I sell my book? 

Just as I have developed my own checklist, authors should develop their own list to determine if a books should be written.

The only common item each list should have is does the book NEED to be written? Not from the author's perspective, but from the perspective of a reader? Will some one buy and read the book?