What is "Reasonably Close?"

I've been thinking about what "reasonably close" means in terms of genealogical research. I have been working on a relative of my wife's in central Missouri: William Rhodus, born around 1830 in Kentucky. He has been located in 1870, 1880, and 1900 census records. I think I have him in the 1860 census as well and I think the match is "reasonably close." I used that phrase in Casefile Clues (William's mentioned in an upcoming issue), but I really am not certain exactly what that phrase means?

How many items about William Rhodus serve to distinguish him from other individuals, his name, his date of birth, his place of birth, his wife, etc.? And how many of those elements much match a potential candidate in order for the candidate to really be considered the William Rhodus and be "reasonably close."

Is it 3 out of 4 items? 5 out of 6 items? Over 75%? I'm not precisely certain and I'm not really certain that "reasonably close" can really  be defined. We'll be discussing more later as I think it is an important topic.