# Total Skill Index

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The Total Skill Index (or TSI) is an official measure of a player's abilities. The formula used for the calculation is unknown, but several somewhat successful attempts have been made in approximating the true function. It is rumoured that HT-Bjorn proclaimed he'll change the TSI calculation formula as soon as someone figures it out.

As a general rule, the higher the TSI, the better the player. However, there are problems with this theory. A player who is average in several skills (e.g. inadequate in defending, passing, and scoring, but with excellent stamina) will often have a higher TSI than a more specialized player (e.g. excellent defending, but everything else poor or lower). TSI also increases with training and it can also increase and decrease with form. Sometimes, TSI will drop even though form does not. This is an easy way of spotting that a background form change has occurred, and the form sub-level has decreased.

TSI for goalkeepers is a different matter. The higher TSI for a keeper, the better. Since a keeper only specializes in one skill, goalkeeping skill can be measured quite accurately based on their TSI and form (e.g. using http://www.hottrick.org/hattrick_keeper_tool.php).

Interestingly, goalkeepers typically have higher TSI at the same skill level than outfield players. A common theory is that both form and stamina have a multiplying effect on the TSI, whereas the other skills (for keepers, goaltending only) contribute as a sum of exponential functions.

Set Pieces and experience do not affect the TSI.

## TSI approximation

For Goalkeepers an approximated formula for TSI calculation is:

```TSI = [(0.025f+0.1)[10(s-1)]^(3.4)]/100
```

With f = Form and s = Skill (1 = disastrous, 2 = wretched, etc.)

For outfield players, the formula for TSI calculation is of the following form:

```TSI = sqrt(f)*sqrt(st)*(A*[pl^3+d^3+sc^3]+B*w^3+C*pa^3)^2
```

With f = Form (1 = disastrous, 2 = wretched, etc.

With st = Stamina skill

With pl = Playmaking skill

With d = Defending skill

With sc = Scoring skill

With w = Winger skill

With pa = Passing skill

With A,B,C being fixed constants (up to you to find them ;-))