In this paper, we propose an improved method (formula) providing a synthetic index for evaluation of both the individual player and the entire team. The method for evaluating of players' efficiency consists in the game's monitoring by experts and an appropriate statistic technique. According to Official Volleyball Statistics Rules [1], several sort of typical actions matter in the game's statistics: the attacks, the assists, the serves, the digs, and the blocks. During the game, few designed observers count and classify the actions outcomes in three categories: (a)-a kill, (b)-the ball stays in play, and (c)-an error. A great deal of information should be marked in the box score. One of the main reasons to improve the method is to reduce as possible as the effort for events acquisition in the match. In order to do this, our goal was to develop a more suitable formula dealing with statistic data. Methods A synthetic play's efficiency index was defined [2] as I= (a2+b)/ [(a+c)2+b]. We propose a corrected formula by a coefficient N=(a+b+c)/ t as follows: I=(a2+Nb)/[(a+c)2+Nb]. The terms a, b and c are numbers of actions in each categories above defined while N is the number of ball is touching in a certain period. The term b denotes the category with a high degree of uncertainty, but it also denotes a spectacular game. As the matter a fact, weighting factor N increases the flexibility of method. This non-linear relationship is more realistic than any other because of time parameter t, which is very important in games. In this manner becomes possible to evaluate the play and/or the efficiency of any player in the significant phases of the match. Results First, we have an interesting interpretation of the proposed formula that exhibits the worst case (the result is zero) and the happy case (the result is one). In Table 1, few possible scenarios are presented. Second, the effect of parameter t on player efficiency is discussed. Theoretically, there is a nonlinear efficiency decreasing versus time for a given game's statistics (a, b, c). In the extended paper, we present a set of analyses based on matches' statistics in training and competition. Discussion / Conclusions The proposed method brings certain advantages: 1. Replaces many other statistic parameters (like hitting percentage and different ratios) by a synthetic one based on only three observed events. The proposed formula is useful in any kind of action (attack, serve, block, etc.). 2. The explicit time in formula allows making remarkable real time analyzes regarding the players/team efficiency. This provides a real improved technical and tactical assistance in training and competition. 3. Based on the proposed united parameter for games efficiency we aim to develop a complex knowledge based system dedicated to volleyball (but not only) games.
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