What percentage of typical web visits are coming from guests with accessibility needs?  

No, we can tell what people are using but we can’t really tell how many. I will tell you that 1 out of every 4 people in the United States has a disability that affects their daily life, 26% according to the CDC. This is not insignificant, these are meaningful numbers of people. There are more people with visual disabilities using the internet in the United States than all internet users in Canada. These are large numbers; it is not something to be taken trivially. It is a large population, not all 26% are going to have a hard time with your website, but what percentage is? 10%, is that an acceptable number? Probably not. But increasing your website usage by 10% is an amazing business number. If I told you, we could increase your website traffic by 10% by making it work for people with visual disabilities you would jump on that number from a business perspective.