Isn't this something of a "duh" kind of result though. The packaging on filters give suggested replace after X days kind of info. Yes, the average person doesn't change filters frequently enough, but people with allergies probably do it more regularly. These types of studies just help explain why the manufacture of the filters suggest estimated time of replacing. I say suggest because the filters I use suggest 90 days, but I live with a cat and no carpet, so it gets clogged much faster than 90 days.