Stuttering is a defined yet non-defined term. You have neurological, genetic and trauma stutterers. I know people who were stuttering (and some cluttering) due dementia at 90 to even 100, is that speech reduction due dementia or straight up stutter (disorder)? A person is stuttering after a very bad traumatic event, that is a heavy stress response, its not directly wired into the brain of the person. Sometimes a person can go years without stuttering after months/some years doing so, and then returning back for some months or even some years, so they haven't a clear picture of the state of their speech. Not everyone is open about it, some people hide it away. And you also have the very light stutterers who still have it, but its the minimal amount of stutters, but they already have a light to mild stutter from the beginning of their speech development. So its very hard to research? So what is stuttering in the noun-form instead the verb-form?