There are many challenges for anyone entering a new field of study or a new discipline. We are all coming into any new concept with all of our previous held knowledge and previous held beliefs filtering and changing how we view the new thing before us. Some choose to make it fit their world view, others dismiss it from fear, and others look for how it can change their current world view. Usually in these situations I quote Sherlock Holmes, “It is a capital mistake to theorize before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts.” Nothing represents this challenge more in online marketing then the differences between analytics and optimization, and nothing represents that struggle more than the debate about visit based measurement versus visitor based measurement.
The debate about should someone use visits, impressions, or visitor basis for analysis is a perfect example of this problem, as it is not as simple as always use one or the other. When you are doing analytics, usually visits are the best way to look at data. When you are doing optimization, there is never a time where visits would present to you more relevant information then using a visitor based view of the data.
Analytics = Visit
Optimization = Visitor
The only possible exceptions are when you are using adaptive learning tools. While the rules can be simple, a deep understanding of the way presents many other opportunities to improve your overall data usage and value derived from every action.
Since most people reading this start in an analytics background, let’s look at what works best in that environment. Analytics is a single data set correlative data metric system, which is a long way of say, it counts things on a consistent basis and only one set of data, even if that data has many different dimensions. You are only recording what was, not what could or should be. In that environment, you have to look at data in some very particular ways. The first amongst those is a very tight control on accuracy, since in many cases the use of that data is to represent what the business did, and to hopefully make predictions about the future.
It is also important that you are consistent with how you measure and that you look at things in a common basis. Because most people are comfortable looking at a day or shorter term basis, this means the easiest method is going to be a visit. It is works great because you are trying to look at interactions and to measure in a raw count of things that did happen, e.g. how many conversions, or how many people came from SEO. In those cases, a raw count in a correlative area is going to be best represented using a visit basis, since it mitigates lost data (though it is not a massive amount) and it best reflects the common basis that people look at data.
In the world of optimization however, you have a completely different usage and type of data. In optimization we are looking at a single comparative data point, and trying to represent an entire different measure, which is influence on behavior over time. It doesn’t matter if your site changes once a year or once an hour, or if your buying cycle is 1 visit or 180 days, all of those things are irrelevant to the fact that you are influencing a population over time. Because behavior is defined as influence on a population, and because we are looking comparatively over time, the measurement techniques used in analytics need to be rethought. Any concern about accuracy, past a simple point, become far less important than a measure of precision (consistency of data collection) since all error derived is going to be equally distributed. It doesn’t matter if the common basis is $4.50 or $487.62, what matters is the relative change based on the controlled factor. It is also important that we are focusing far more on the influence then the raw count, which means we are really talking about the behavior of the population.
In analytics you are thinking in terms of, what was the count of the outcome (rate) as opposed to in optimization the focus is on what was the influence (value). To really understand optimization, you have to understand that all groups start with a standard propensity of action which is represented by your control group. If you do nothing the people coming to your site, people in all stages and all types of interaction, measure up to one standard measure across your site (though all measurement systems do have internal variance in a small degree). Since we are measuring not what the propensity of action is but what are ability to positively or negatively influence it is, we need to think in terms of reporting based on visitors and based on the change (lift) and not the raw count.
You also have the case of time, where we need to measure total impact over time. While it is correct that every time a visitor hits your site you have a chance to influence them, it is important to remember that the existing propensity of action measurement already accounts for this. What we are looking for is a simple measure of what did we accomplish by in terms of getting them to spend more. This means that we have to think in terms of both long and short term behavior. Some people will purchase today, some 3 visits later, but all of that is part of standard business as usual. It is incredibly easy to have scenarios where you get more immediate actions but less long term actions. This means that on a daily basis you might see a short term spike, but for the business overall you are going to be making actually less revenue. This possibility creates two possible measurement scenarios:
1) There is no difference between short term and long term behavior, meaning the short term spike continues through and is positive also in the long term. In this scenario the only way to know that is to look at the long term.
2) There is a difference and short and long term behaviors differ and we are getting a different outcome by looking at the visitor metric over time. In this scenario the only positive outcome for the business is the visitor based metric view.
In both cases the visitor based metric view gives us the full picture of what is good for the business, while the visit based metric system either has no additional value or a negative value by reaching a false conclusion. In either case the only measure that adds value and gives us a full picture is the visitor based view of the world. We have a case where visitor is both the most complete view, no matter the situation, but the only one that can give you a rational view of the impact of a change. To top it off, the choice to only look at the shorter window creates a distribution bias, by valuing short term behavior over long term behavior, which may create questions into the relevance of the data used to make any conclusion.
The visitor vs. visit based view of the world is just one of many massive differences that reduce the value derived from optimization if not understood or not evaluated as a separate discipline. Because it is so easy to rationalize sticking with what is comfortable, it is common to find this massive weakness being propagated throughout organizations with no measure of what the cost really is. While not as damaging as others, like not having a single success metric or not understanding variance, it is vital that you are thinking about visit and visitor based data as attached the end goal and not as a single answer to everything.
In the end, the debate about which version to use is not really one about visits or visitors, there are clear reasons to choose visits for analytics and visitor for optimization. The real challenge is if you and your organization understand the different data disciplines that are being leveraged. If you constantly look for different ways to think about each action you will find new and better ways to improve value, if you fail to do so you will cause damage throughout your organization and will not even know you are doing it.