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How did I come up with my free-agency grades for players?

I've been asked that bunch on Twitter, and I've also been asked how I can have such different ratings than those of our Pat Kirwan, who also ranked his top 150 free agents here at CBSSports.com.

Here's what I do when I look at free agents: I look at productivity going forward, which means age matters. So when I graded each of the 150 players, I took that into account.

As a general manager, I wouldn't want to spend on a guy whose best football is behind him. I'd pay based on what's to come, not what has already happened.

So that's the basic tenet for how I rank players. It's not what you did just last year, but what you can do going forward.

I think that's why you see some disparity between my rankings and Kirwan's rankings. Take Minnesota defensive end Jared Allen. Kirwan gave him a rating of 82. I gave him 69. 

I do think Allen, who is 32, can help for a year or two, but in terms of ranking on a free-agent list, he's too old for my liking -- thus, the lower ranking. 

Jared Allen's age must be considered when rating his free-agent worth. (USATSI)
Jared Allen's age must be considered when rating his free-agent worth. (USATSI)

I gave Green Bay corner Sam Shields a grade of 84, while Kirwan gave him a grade of 59. Shields is 26 years old and a good cover corner. I think his best football is in front of him, and he plays a value position, which is why he received the high grade from me.

Kirwan gave Vontae Leach, a 32-year-old fullback, a nice grade of 60. I gave him a 39. Why? You can find fullbacks in the draft, and he's old. Bad combination.

So as you look through our grades here on our free-agency list, just remember I grade on future value, not the past. A player could be coming off a big season, but if he's older, and his career is winding down, he doesn't warrant a big grade on my list. That isn't always the case, depending on the position, but most of the time. 

For the most part, I like my top-rated players to be in the 26-29 age bracket. That's when the best football is usually played.