@conference {kountouris2009expressions, title = {Expressions of skill effectiveness that are more congruent with the team performance in Volleyball.}, booktitle = {11th International Conference of Sport Kinetics. 25{\textendash}27 September 2009. Halkidiki, Greece.}, year = {2009}, abstract = {

EXPRESSIONS OF SKILL EFFECTIVENESS THAT ARE MORE CONGRUENT WITH TEAM PERFORMANCE IN VOLLEYBALL.

Kountouris. P., Laios. Y., Drikos. S., Laios. A.

Faculty of Physical Education and Sport Science, University of Athens

The identification and quantification of the most consequential factors in reflecting the overall team{\textquoteright}s performance is of primary importance in every team sport. In Volleyball it is obvious that these factors should be sought within those skills that lead to either winning or losing the specific rally. The aim of the present study was to determine whether latent derivative parameters, computed from relative proportions of decisive actions that lead immediately to winning or losing the rally, can be better predictors of team{\textquoteright}s performance in Volleyball.\ Data were collected over eight seasons (2000-2008) of the Greek Men{\textquoteright}s Volleyball Championships. For each season the overall statistics for each of the twelve teams were calculated. The original independent variables were proportions of actions that immediately led to winning or losing the rally to the total number of these actions: serve aces, serve errors, kill attacks and attack errors. From these two new variables were derived: the serve efficiency ratio (SER), which is the ratio of serve errors to serve aces, and the attack efficiency ratio (AER) which is the difference between the proportion of kill attacks and attack errors. The primary dependent variable is the set ratio (SR), which is the number of sets won divided by the total number of set played by the team. Pearson{\textquoteright}s correlation coefficients were calculated between the dependent and the independent variables. The teams were also divided into two groups: teams with SR<=0.5 and teams with SR\>0.5 and the derived variables were tested with Student{\textquoteright}s t-test.\ SR does not correlate with the proportion of lost serves (r=0.037), but correlates well with the proportion of serve aces (r=0.589) and even better with SER (r=-0.661). Also the correlation coefficient between the proportions of serves errors and serve aces is quite high (r=0.530). The mean value of SER for teams with SR\>0.5 is 2.3{\textpm}0.5, while for teams with SR<=0.5 it is 3.0{\textpm}0.6 (t-test, p\<0.01). SR has a significant negative correlation with the proportion of lost attacks (r=-0.694) and an even higher positive correlation coefficient with the proportion of attack kills (r=0.819). Again SR correlates best with AER (r=0.851). The mean value of AER for teams with SR<=0.5 is 29.4\%{\textpm}3.7\%, while for teams with SR\>0.5 it is 36.1\%{\textpm}4.6 (t-test, p\<0.01). The fact that the proportion of serve errors correlates highly with the proportion of serve aces can be founded on the nearly universal trend in modern Volleyball towards jump serves. These serves certainly have higher prospects to win a serve ace, or at least to encumber the opposing team{\textquoteright}s reception. At the same time they undoubtedly entail a higher risk of execution. Teams that did not perform well managed on the average only one serve ace per three serve errors and their AER was less than 30\%, while the for the teams that performed better the SER was nearer to two and the AER was more than 35\%. Therefore the overall team{\textquoteright}s performance in Volleyball can be better predicted by quantifiable combinations of its actions with both positive and negative outcome.

}, author = {Kountouris, P and Laios, Y and S Drikos and Laios, A} }