As others have stated, no one outside of the NW Team who manages the upgrade process knows the real story. But based on past experience with what we call "Battlefield Upgrades" or "The Gate Lottery" (upgrades you have to wait to receive at the gate just prior to departure)... my guess as to "the magic formula" would be a pecking order something like this:

1 & 2) Plat Full Fare PAX + Full Fare Companion (If Applicable)
3 & 4) Gold Full Fare PAX + Full Fare Companion (If Applicable)
5) Silver Full Fare PAX
7 & 8) Plat PAX (ordered by discount fare paid, then earliest booked flight, then earliest checked in @ 24 hours) + Companion (If Applicable)
9 & 10) Gold PAX (ordered by discount fare paid, then earliest booked flight, then earliest checked in @ 24 hours) + Companion (If Applicable)
11) Silver PAX (ordered by discount fare paid, then earliest booked flight, then earliest checked in @ 24 hours)

This is my guess as to the formula. Other criteria that NW might be considering is lifetime miles, and your seniority date on the WP program -- but my guess is that they use the other criteria (fare, date booked, and check-in time) first.

-A

Do you really think a Plat or Gold companion will get the upgrade ahead of a Plat? I thought that only companions got the upgrade after other members in the same status got it, regardless of whether the Plat paid full fare or not.

Plat full fare
Plat
Plat full fare companion
etc.

I think the plat companions would get that priority at the window, but at the airport I'm pretty sure they're at the end of the list.

I suspect that they don't use fare class other than full/discount. I was on a recent superpeak flight on a K fare, and I heard lots of plats grumbling about being in the back -- as I headed for 1D.

I think that Poopdeck 90210 is correct about lifetime miles having some weight. I have noticed I do get to the top of the list frequently (not always) regardless of check in time. But then again, there are times when I've been told "14 plats on the wait list don't bother". Does anyone really know how the software sets it's priorities.

Of course, Northwest could mitigate the problem by installing more seats in F. It's a big difference between 16 first class seats and 22. Again though, the majority of agents have told me the wait list (within categories) is solely determined by check-in time.