The formula can even be applied to individual spotsin cases where a media vehicle might not have its reach measuredto estimate reach. A buy that has a large number of cable spots, all of which do very low ratings, could be estimated. For example, lets say we purchase 400 cable spots with an average rating of 0.1. We can estimate Cn = 1 ((1-a)^400) so that each spot has a 0.1 percent reach. This, when elevated to the number of spots purchased, gives us the estimated combined reach.
Cn = 1-((1-.1%)^400 = 33%
So our 400 spots would have a combined reach of 33 percent.
A second way to look at the Sainsbury model is to see the contribution that each vehicle or medium makes to the entire plan.
Basically, if the audience of A is 45 percent of the audience of B, Bs contribution is only 19 percent of its reach; Cs contribution is only 8.3 percent of its 30 percent reach, etc. You can see this too in real life: The more media we add to a schedule, the less reach that each medium adds. After all, there is a finite number of people in any universe.
There are three important factors to consider when using these formulas:
1. They are not 100 percent accurate. Then again, unless you have actual research, it is impossible to have really 100 percent accurate research. But it is not 100 percent inaccurate either. Several studies show a decent accuracy.
2. They are easy, quick and flexible tools that can be implemented on the fly to try out different schedules.
3. By being purely intellectual, these tools preserve our strategic view and avoid getting us bogged down in details.
Communication evaluation. As we work our way through the channel strategy, a real concern we need to face is the ability of each medium to communicate the product’s key points.
Most creatives will argue that any medium can communicate any point as long as the creative is right. However, in real life, it is hard to communicate a demo on a billboard, for example, or huge amounts of text on television. At best, having a communication evaluation model allows us to fine tune our media strategy. At worst, it should spark the creative juices to find solutions within a budget.