Sure, we’ve got seven years of evidence!
Put simply, there are privacy implementations and ad blockers installed on many personal computers as well as inboxe apps/services that are used to track opens and clicks and such. Some use essentially tracking pixels (an image), some use some sort of script or code, and some use their own methodology.
But if that image doesn’t load, or if the script doesn’t fire, or the technology just doesn’t work for a minute, that open or click is not returned to the server. Even if it is, tracking opens is a notoriously difficult process that is far from perfect.
What this means is there could be people opening your email that you never know are opening it, and you want to just mark them inactive or "cull" them because you think it’s going to help your open rate.
Somewhere along the line we started to hear “culling your mailing list and deleting inactive subscribers will improve your open rate,“ but what we actually heard was "culling your mailing list will increase the number of people who open your email."
But these are not the same thing at all. If I have 100 people on my list and 25 people open an email, that’s a 25% open rate (duh!). If I increase my list size to 200 subscribers, and 40 people open my next email, that’s a decreased open rate (20%), even though the actual number of opens increased.
See the difference? The only reason to remove people who appear to be inactive is either because 1. you want a higher percentage open rate to feel better about that number or 2. because you’re paying a lot of money for those folks to hang out on your list and (ostensibly) not do anything.
My answer is simple: never "cull" a list — just get a cheaper email service!