The basic ROI formula is:
ROI = (Gain from Investment-Cost of Investment) / Cost of Investment
So, the ROI formula contains three components:
- Gain from Investment
- Cost of Investment
- Time - Although the formula doesn't expressly contain a "time" value, ROI is always measured for a defined period of time.
For ROI purposes, the best definition of Gain from Investment is the incremental contribution margin produced by the marketing function or by a marketing campaign or program. One of the biggest mistakes that I still see some marketers make is to use incremental sales (revenues) to calculate marketing ROI.
To understand why this mistake distorts ROI, remember that most marketing programs are designed to increase sales volume either by acquiring new customers or by increasing sales to existing customers. But increases in sales volume are not free - there is always an associated cost of producing and delivering the additional products or services. Therefore, if incremental sales are used to measure ROI, the ROI will be overstated.
Using contribution margin solves this problem by taking costs into account. Contribution margin is defined as sales minus variable costs. Variable costs are costs that the company will not incur if the additional sales are not made. Therefore, incremental contribution margin is a measure of the "net new revenues" produced by a marketing program.
The second major issue presented by the Gain from Investment component of the ROI formula is how to address situations where the Gain may have been produced by more than one marketing campaign or program. This situation is not at all uncommon in B2B companies where each prospect may be "touched" by several marketing programs over the course of his/her buying cycle.
Some companies deal with issue by assigning all of the incremental contribution margin earned from a prospect to the marketing program that generated the first "inquiry" from that prospect. Others assign all of the incremental margin to the program that "touched" the prospect last (just before the purchase). It should be obvious that this first touch/last touch approach will often produce a distorted picture of marketing ROI if a prospect has had several interactions with your company.
Some companies attempt to eliminate this distortion by allocating the Gain to all of the marketing programs that "touched" the prospect. But what percentage of the Gain do you assign to each program? Allocating the Gain equally to all of the marketing programs may not reflect which of the programs were truly influential in the purchase decision and which ones weren't. Unless you have some way of knowing how much influence each program actually had in driving the purchase decision, the allocations are arbitrary, and the resulting ROI measurement is likely to be inaccurate.
This allocation issue presents one of the most serious challenges in measuring marketing ROI accurately, especially when we attempt to measure marketing ROI at a very grandular level. The difficulty of using ROI in this way suggests that there may be a better approach, and I'll have more to say about that in a later post.