After last week’s post on how long it will take for your book to deliver a profit, I started thinking. How do you actually calculate your book’s ROI?
The short answer? It’s complicated.
I’ve written before about the Zero Moment of Truth and how most people don’t buy from you the first time they interact with you. This means that means your return rarely comes down to a single moment.
Your customers’ path to purchase
According a study run by Google in 2011, it takes the average customer needs to interact with you:
(More on what these terms mean here.) Rather than someone buying your book and immediately choosing to buy a higher priced product or service, they are also likely to:
My team and I see this all the time at Grammar Factory, where the steps someone takes before working with us could be as simple as this:

Or more complex, like this:

(Note that someone might be receiving weekly emails for 6-12 months before they reach out to chat, and at the same time they might also be following us on Facebook, Instagram, Twitter and/or LinkedIn, and may come along to speaking engagements and other events.)
So the question is: If the average customer interacts with your business 11 separate times before deciding to work with you, how do you calculate the return on any of the steps in that mix?
This brings us to attribution modelling.
Attribution modelling
Attribution modelling refers to how much weight you assign to each step along the journey your customers take from discovering you to deciding to buy from you.
There are five common attribution models that big companies tend to use – these models help them define the return on their marketing efforts, as well as how much they should invest in different types of marketing. The five models are:
(Note that these models are usually used in an online analytics environment, but the theory holds true for the customer journey in general, whether that journey occurs online, offline, or has both on- and offline steps.)
Last interaction
Last interaction assigns 100% of the value of the sale to the last step a customer takes before deciding to work with you.
In other words, if a customer follows you on Facebook, reads five emails, buys your book, has a phone call with you and then decides to buy a $10,000 package from you, that final phone call would get 100% of the value of that sale. The phone call is valued at $10,000, while no value is assigned to any other steps in the journey.

First interaction
First interaction, on the other hand, assigns 100% of the value of the sale to the first step a customer takes in the journey.
To continue the previous example, if a customer follows you on Facebook, reads five emails, buys your book, has a phone call with you and then decides to buy a $10,000 package from you, Facebook you would get 100% of the value of that sale.

Linear
If you’re using a linear attribution model, every step on the journey would be given the same value. So in a five-step journey to a $10,000 sale, each step would be valued at $2,000.

Position based
The position-based model assigns a unique value at each touch point, with greater value to the first and last steps in the journey. The most common approach (the bathtub model), divides 80% of the conversion value between the first and last step, with the remaining 20% divided between the middle steps.
If we return to the early journey I outlined, the steps were:
- 1Facebook follow
- 2Read email 1
- 3Read email 2
- 4Read email 3
- 5Read email 4
- 6Read email 5
- 7Buy your book
- 8