Reference
What is visibility?
The method of comparing the incomparable
What is visibility and how do we calculate it
Visibility is the parameter which illustrates how many visits a website can potentially get due to searches. To calculate visibility we use data on search volume of keywords for which a website holds high positions, data on these positions and ratios for positions it occupies.

Let's illustrate the meaning of this parameter with an example. Let's imagine two websites, each of which is represented in search results just by a single keyword.
"A" website holds the first position for the "buy plastic windows in Balashikha cheaply" keyword. Let's say the search volume of this keyword equals 10.
"B" website holds the ninth position for the "buy plastic windows" keyword, and search volume of this keyword equals 5000.
Our example is quite graphic, "B" website clearly has greater potential of attracting visits, but how to express that numerically?
To make comparison of such combinations possible, we've developed our algorithm for calculating website visibility. We set a specific ratio for each position, which in practice reflects probability of a user clicking on a website which holds this position.
For example for the 1st position the ratio is 0.7 (70% of users would click), and for the 9th position the ratio is 0.15 (only 15% of users would click).
For example for the 1st position the ratio is 0.7 (70% of users would click), and for the 9th position the ratio is 0.15 (only 15% of users would click).

Then we multiply search volume of a keyword by this ratio and see that "A" website will get roughly 10*0.7 = 8 visitors per month, while "B" website will get 5000*0.15 = roughly 750. Therefore "B" website will get nearly 100 times more visitors, even though its average position in search results is lower.

Then we can summarize results of multiplying a keyword's search volume by its position ratio for all keywords of each website, and conclude which website has the greater potential for getting visits.