Lateness factor for a given person is defined as followed. Simply ask the person's significant other (or if single, best friend) to translate various arrival time predictions and apply the following rules:
If they translate "definitely"or "for sure" or "will be" to "probably", add a point
If they translate "probably" to "maybe" or "might be", add a point
For every half hour of lateness they assume, add a point
The sum of this scoring system is the Lateness Factor. For example, I've decided Danielle's current lateness factor is about 2 (she used to be a zero, for the record...much like athletic performance, I predict lateness factor will change for the worse with age), which means her text of "I'll definitely be home by 5" could translate into any of the following:
1. I'll definitely be home by 6
2. I'll probably be home by 5:30
3. I might be home by 5
Obviously the higher the lateness factor, the more possible translations exist, but practically speaking the statistic really only has meaning from values of about negative one to three (the big potato almost certainly has a negative lateness factor; if I schedule a lunch for 12pm, he will definitely be there by 11:30). Values outside of that range are pretty much useless, as they indicate a basic disdain for any sort of scheduling whatsoever.
Mildly Related Tangent
Most people use the commonly accepted scoring system of 1 to 10 to gauge a person's attractiveness (the poster formerly known as cgrohman prefers a binary 1 or 0 scoring system, but many feel this is short sighted). What does this mean? People aren't really sure, but here is my interpretation, specifically that it is a log scale:
These people are merely mildly pleasing or displeasing to the eyes. They are in short average.
These people are "1 in 10s", meaning that saying someone is a seven means that roughly speaking if you saw 10 other people on the street, you'd expect one of them to be about as attractive as said person (just the opposite for a 4).
Same deal, except 1 in a 100. So someone who rates an 8 is reasonably likely to be the most attractive person of a group of 100. A 3 would likely be the homeliest.
Same deal, but 1 in a 1,000.
Same deal, but 1 in 10,000. In short, at a large university like, say, Penn State, with 30K undergrads, there should only be 1 or 2 women you'd rate as a 10.