Psycho Stats calculates skill value for each player based on who a player kills. The total number of kills or deaths you have, or the weapons you use, or how much time you've played do not matter. This type of skill calculation works really well for determining who is best.

Every player starts with 1000 skill points. And everytime you kill someone your skill is recalculated to include the points for the new kill.

The basic formula when killing someone and gaining points is shown below.
(note: K = The killer, V = The victim.

K = K + ((V / K) * 10)

Example; assume K = 1000 and V = 2000. If you do the math, the killer would get 20 points for the kill. since the Victim had a much higher skill then the killer. Reverse the skill points so that the Killer had 2000 and the Victim had 1000 and the Killer would only get 5 points for the kill. As you can see, when you kill someone with a higher skill point value then yourself you get more points. And this makes since, seeing as how someone with a higher skill is going to be harder to kill.

When you get killed you lose points depending on your current skill points. If you have 2000+ skill then you will lose the same number of points that the killer gained (which is usually more then 10). Otherwise if you had less then 2000 points then you get a flat reduction of 10 points.

if (V < 2000) then
   V = V - 10
else
   V = V - ((V / K) * 10)

Generally will will not see very many people with 2000+ skill points, which is why people that have that much skill are reduced more then other players. People that do obtain that value should be considered very good players. The highest I've ever seen anyone get is about 2200 skill points.