IDENTIFICATION OF FACTORS DETERMINING WINNING IN MEN’S AND WOMEN’S BEACH VOLLEYBALL: A LOGISTICAL REGRESSION APPROACH

The purpose of this study was to find the factors responsible for winning in the men’s and women’s beach volleyball championship. Materials and methods. The study sample consisted of a total of 212 matches for men and 214 matches for women of the 2017 & 2019 FIVB Men and Women Beach Volleyball World Championships held at Vienna & Hamburg from 28 July to 6 Aug 2017 and 28 June to 7 July 2019. The matches were played by 192 teams (both men and women combined) consisting of 384 numbers (both men and women combined) of players from different nations. The data were analyzed using Binary Logistic Regression (Forward: LR Method) with the result of the game as the dependent variable and predictor variables as covariates. β, standard error β, Wald’s χ2, odds ratio with 95% confidence interval were calculated. Model evaluation was conducted using the likelihood ratio test, Cox & Snell (R2), and Nagelkerke (R2) tests. The goodness of fit test for the models was conducted using the Hosmer & Lemeshow test. Results. The analysis revealed seven factors related to winning in men’s and women’s competition. While in league rounds, six factors in men’s and seven factors in women’s competition were related to winning. Besides, in knockout rounds, four factors in men’s and six factors in women’s competition were related to winning. Conclusion. The study shows that there is a significant association of important factors with respect to winning a match in an elite beach volleyball championship. The coaches and players can take note of the important factors responsible for winning in the elite beach volleyball championship, with different factors playing an important role in men’s and women’s competition during league and knockout rounds as well.


Introduction
Beach volleyball has developed from a recreational activity to a professional sport over the last few decades. Since its inclusion in the Olympics in the 1996 Atlanta Summer Olympic Games, the game has shown tremendous growth in popularity all over the world. Beach volleyball is an intermittent sport played by teams of two players in a sand court and demanding powerful short rallies interspersed by pauses or less intense activities. Matches are characterized by repeatedjumps for attack-hit and block, rapid changes in moving direction, and a considerable number of explosive diving digs (Magalhães, Inácio, Oliveira, Ribeiro, & Ascensão, 2011).
The major skills which characterize the game of Beach volleyball are: serve, serve reception, set, attack, block, and dig (Hare & Sanderson, 1997;Homberg & Papageorgiou, 1995;Kiraly & Shewman, 1999;Stevenson & Obstfeld, 1989). Serve, attack and block give direct score points to the team, whereas serve reception, set, and dig allows for the next technical skills (Giatsis & Zahariadis, 2008). The game has two phases: side out and counterattack. The side out phase includes serve reception, setting, and dig & the counterattack phase includes block, dig, set, and attack (Costa, Afonso, Brant, & Mesquita, 2012).
Researchers have always been keen to analyze and evaluate technical and tactical aspects of the team's performances in various sports. The characteristics of the beach volleyball game have been previously studied (Hansen, 2002;Hömberg & Papageorgiou, 1995;Papageorgiou & Hömberg, 2004), but sports are in constant evolution and it is necessary to analyze them on a regular basis. In 2001, rules on court size and the scoring system changed, which led authors to research how this affected the game. Some studies investigated court size ТМФВ, 2021, том 21, № 1 Kumar, G., Shukla, A., Chhoker, A., & Thapa, R. K. (2021). Identification of Factors Determining Winning in Men's and Women's Beach Volleyball: a Logistical Regression Approach (Giatsis, Papadopoulou, Dimitrov, & Likesas, 2003;Hömberg & Papageorgiou, 1995;Kröger, 2006;Ronglan & Grydeland, 2006) and others focused on the scoring system (Giatsis, Zetou, & Tzetzis, 2005;Kröger, 2006;Ronglan & Grydeland, 2006). Furthermore, some studies analyzed technical and tactical aspects such as side out and counter-attack phases, receptions, and differences between winning and losing teams (Giatsis, Lopez Martinez, & García, 2015;Giatsis & Tzetzis, 2003;Michalopoulou, Papadimitriou, Lignos, Taxildaris, & Antoniou, 2005). A study conducted by Giatsis and Tzetzis (2003) postulates the different technical skills contribute to winning on different court dimensions (8x9m and 9x9m) in Hellenic Beach Volleyball finals. The results showed that winners have a better percentage in the attack in 8x8m, while they had better serve reception performance in the 9x9m court. Traditionally, coaching intervention has been based on subjective observations of athletes, but such observations are not only unreliable but also inaccurate (Huges & Franks, 2010). To solve this issue, computer-aided analysis has been involved in sports performance analysis. The use of notational analysis (Castro, Souza, & Mesquita, 2011;Marcelino, Mesquita, & Sampaio, 2011) and computerized systems (Eom & Schutz, 1992a, 1992b is the most common methodology in sports performance studies, which had improved the speed, accuracy, and efficiency of data analysis. Notational analysis is the process of recording, treatment, and diagnostics of events taking place in a competition (Drust, 2010). Several studies have been conducted on the notational analysis of technical and tactical aspects of volleyball (Ciuffarella et al., 2013) and beach volleyball (Jimenez-Olmedo, Penichet-Tomas, Saiz-Colomina, Martinez-Carbonell, & Jove-Tossi, 2012;Koch & Tilp, 2009b;Pérez-Turpin et al., 2019;Tilp, Koch, Stifter, & Ruppert, 2006). It has facilitated coaches in the analysis of movement patterns, strategy, and tactics of the individual player as well as the team's performance.
Although numerous studies have been published related to Beach volleyball (Giatsis & Zahariadis, 2008;Koch & Tilp, 2009a;Papadopoulou, Giatsis, Billis, Giannako, & Bakirtzoglou, 2020;Seweryniak, Mroczek, & Łukasik, 2013), only a few have been published regarding the factors responsible for winning and losing in Beach volleyball for men and women (Gabrio, 2021;Giatsis & Tzetzis, 2003;Medeiros, Marcelino, Mesquita, & Palao, 2017). As the game of beach volleyball is showing an exponential competitive growth pattern, technical skills that are key for success in this game are need to be researched and focused on so that the teams and coaches can prepare themselves accordingly. Therefore, the purpose of this study was to identify the factors which determine winning in a beach volleyball game for men as well as women using a logistical regression approach.

Materials and methods
To identify the factors which determine the winning of a beach volleyball game the matches played during the FIVB Beach Volleyball Men and Women World Championships of 2017 and 2019 were considered in this study. The study variables selected for analyses were the break point, service error, service point, reception error, attack error, attack blocked, attack point, attack point percent, block, and opponent error (Table 1).

Subjects
The study sample consisted of a total of 212 matches for men and 214 matches for women of the 2017 & 2019 FIVB Men and Women Beach Volleyball World Championships held at Vienna & Hamburg from 28 July to 6 Aug 2017 and 28 June to 7 July 2019. The matches were played by 192 teams (both men and women combined) consisting of 384 numbers (both men and women combined) of players from different nations. The data for the present study was extracted from the official website of FIVB (http://vienna2017.fivb.com/en/ schedule#/d20170806) for 2017 for Beach Volleyball World Championship and (http://hamburg2019.fivb.com/en/ schedule#/d20190708) for the 2019 Beach Volleyball World Championship.

Statistical Analysis
All the statistical analyses were performed with IBM SPSS (version 20.0.0). The data were analyzed using Binary Logistic Regression (Forward: LR Method) with the result of the game as the dependent variable and predictor variables as covariates. β, standard error β, Wald's χ 2 , odds ratio with 95% confidence interval were calculated. Model evaluation was conducted using the likelihood ratio test, Cox & Snell (R 2 ), and Nagelkerke (R 2 ) tests. test. In addition, observed and predicted frequencies by the regression model were also calculated with a cut-off of 0.50. The statistical level of significance was set at p ≤ 0.05.

Men
A total of 424 observations were analyzed for men and the logistic regression analysis found the following variables as significant in determining the model for winning of matches: break point, service point, reception error, attack error, attack point percentage, block, and opponent error. The Likelihood ratio test of the model resulted in χ 2 value of 324.29 with p < 0.001. In addition, the Cox and Snell re-     In addition, the total observations were further subgrouped into the league and knockout stages and analyzed. The following variables were found significant in determining the model for winning league matches: break point, reception error, attack blocked, attack point, block, and opposition error. The Likelihood ratio test of the model resulted in a χ 2 value of 308 with p < 0.001. In addition, the Cox and Snell resulted in an R 2 value of 0.582 and Nagelkerke resulted in an R 2 value of 0.785. The goodness of fit test using Hosmer and Lemeshow resulted in a p-value of 0.302 (Table 4). The overall correct predicted percentage using the model was found to be 87.6% (Table 5, Figure 1c).
In knockout matches following variables were found significant in determining the model: break point, reception error, attack error, and attack point.   1993-7989 (print). ISSN 1993-7997 (online). Теорія та методика фізичного виховання. Том 21, №1 The Likelihood ratio test of the model resulted in a χ 2 value of 59.498 with p < 0.001. In addition, the Cox and Snell resulted in an R 2 value of 0.538 and Nagelkerke resulted in an R 2 value of 0.718. The goodness of fit test using Hosmer and Lemeshow resulted in a p-value of 0.122 (Table 6). The overall correct predicted percentage using the model was found to be 85.7% (Table 7, Figure 1e).

Women
A total of 428 observations were analyzed for women and the logistic regression analysis found the following factors as significant in determining the model for wining of the match: break point, reception error, attack error, attack blocked, attack point percent, block, and opponent error.
In addition, the total observations were further subgrouped into the league and knockout stages and analyzed. The following variables were found significant in determining the model for winning league matches: break point, re-ception error, attack error, attack point percentage, attack point, and opposition error. The Likelihood ratio test of the model resulted in a χ 2 value of 287.509 with p < 0.001. In addition, the Cox and Snell resulted in an R 2 value of 0.544 and Nagelkerke resulted in an R 2 value of 0.726. The goodness of fit test using Hosmer and Lemeshow resulted in a p-value of 0.012 (Table 4). The overall correct predicted percentage using the model was found to be 88.3% (Table 5, Figure 1d).
In knockout matches following variables were found significant in determining the model: break point, service point, reception error, attack error, attack blocked, attack point, and opposition error. The Likelihood ratio test of the model resulted in a χ 2 value of 63.929 with p < 0.001. In addition, the Cox and Snell resulted in an R 2 value of 0.643 and Nagelkerke resulted in an R 2 value of 0.858. The goodness of fit test using Hosmer and Lemeshow resulted in a p-value of 1 (Table 6). The overall correct predicted percentage using the model was found to be 91.9% (Table 7, Figure 1f). ТМФВ, 2021, том 21, № 1 Kumar, G., Shukla, A., Chhoker, A., & Thapa, R. K. (2021). Identification of Factors Determining Winning in Men's and Women's Beach Volleyball: a Logistical Regression Approach

Discussion
The purpose of this study was to identify important skill related factors that were significantly responsible for winning in the beach volleyball championships using a logistic regression approach. A forward step method indicated seven factors (out of ten) were related to winning in men's competition. In addition, five factors were positively related (break point, service point, attack point percentage, block, opponent error) while two factors (reception error and attack error) were negatively related to winning. In the case of women's competition, a forward step method indicated seven factors (out of ten) were related to winning. In addition, four factors (break point, attack point percentage, block, and opposition error) were positively related while three factors (reception error, attack error, and attacked blocked) were negatively related to winning.
Further classification of the observations into the league and knockout rounds resulted in an indication of six factors (out of ten) related to winning in the league round, while four factors (out of ten) were related to winning in knock out round in men's competition. In the case of women's competition, six factors (out of ten) were related to winning in the league round, and seven factors (out of ten) were related to winning in the knockout round.
Our study suggests few factors to be significantly responsible for winning in beach volleyball competition, such as break point, service point, attack point percentage, block, opponent's error, reception error, attack error, and attack blocked. Break points include one's own service aces, counterattack points, and a number of winning blocks, and the opponent's errors, although these factors did not explain the ТМФВ, 2021, том 21, № 1 ISSN 1993-7989 (print). ISSN 1993-7997 (online). Теорія та методика фізичного виховання. Том 21, №1 outcomes of matches by themselves in our model. In this competition, the number of points obtained in the break point phase was the factor that made the greatest contribution to the final outcomes. This factor is completely related to the performance of the opponent's reception and the opponent's attack (Peña, Rodríguez-Guerra, Buscà, & Serra, 2013). The service point was also found to be an important factor in determining success in both men and women beach volleyball competition. A previous similar study conducted on volleyball supports our findings (Silva, Lacerda, & João, 2014). The teams are evenly balanced at the world championship level, and when the match gets close to end the serve skill may be associated with victory. The service is the only moment of the game when the players have 100% control over the ball and the way events unfold. The players need to choose the type of service, the force, and the area of the opponent's court to which the service will be directed (Martinez & Abreu, 2003). Service is an opportunity to create the maximum number of problems for the receiving opponent and also score a direct point if possible. Thus, the service is the team's one of the most pre-eminent offensive weapons, causing a range of problems for the receiving team, restricting, forestalling, and even eliminating the possibility of an effective attack on the part of the opponents. A study by Quiroga et al. (2012) analyzed 1300 services and divided them into four components. The components with the greatest influence were related to the type of service used, highlighting the importance of the technical execution and the characteristics of the chosen action, as well as the speed imparted to the service ball. It was found that the players tried to execute a service that secures a direct point or that at least impedes the opposing team from mounting an attack, and to this end, they aim for a service that is accurate, difficult to receive, and very often powerful. The points gained through attack were also found to be the most important skill in volleyball (Lobietti, Di Michele, & Merni, 2006). A previous study also found a significant association between the attack efficiency and the set outcome (Monteiro, Mesquita, & Marcelino, 2009). The reason may be that the teams that win the sets make fewer errors and have higher efficiency in the counter attack. In the similar vein, the attack error and attacks blocked also plays a significant role in winning a match in beach volleyball.
Blocking is an important skill in any format of volleyball to stop the attack at the net and blocking successfully is one of the crucial features of winning in volleyball (Lobietti, 2009). Previous studies (Lobietti et al., 2006) also investigated the importance of block to win the game using cluster analysis in the Italian volleyball professional league and results suggest the block to be the second most important skill after the attack. The points gained using block were also found to be highly correlated to the final ranking (Lobietti et al., 2006). The nature of every sport is such that teams try to find the weaker link in the opponent team to gain benefits. Team tactics are always such that the opponents are forced to commit an error. Our study findings suggest that the opponent's error is linked to winning in elite beach volleyball competition. Previous studies suggest the quality of reception as an important factor in winning a volleyball match (Paulo, Zaal, Fonseca, & Araújo, 2016;Peña et al., 2013;Silva et al., 2014). During the reception, many task-related functional constraints might influence the behavior of the receiver (Barsingerhorn, Zaal, De Poel, & Pepping, 2013). The jump-float serve takes about 1 second to reach the receiver, who needs about 300 milliseconds to initiate his first movement (Benerink, Bootsma, & Zaal, 2015). The receiver's position and movement have effects on how to pass a serve (Paulo et al., 2016), and a player not able to flexibly adapt to varying constraints results in loosing points.
Differences between winning and losing teams have been of particular interest to researchers, and previous studies indicate that attack efficiency and error percentage were the primary factors in winning a match (Giatsis & Zahariadis, 2008;Michalopoulou et al., 2005). This could explain why there is more offensive than defensive movements and vertical advance movements in professional women's beach volleyball (Pérez-Turpin, Cortell-Tormo, Suárez-Llorca, Chinchilla-Mira, & Cejuela-Anta, 2009).
In addition to this, there was some significant reflection in our findings when the observations were further divided based on league matches or knockout matches. In men's competition, six factors were found to significantly affect the winning of matches in the league round, whereas only four factors were found significant in knockout rounds. One reason for this finding may be attributed to the fact that only the best teams qualify to the knockout rounds through the league matches. With the best teams playing in the knockout stages, it becomes evident that only a few factors will be contributing to the winning. Giatsis and Zahariadis (2008) could observe that 2:0 winning teams on an international level (FIVB) have superior skills in almost all techniques, especially in avoiding attack errors. During close games (2:1 wins) only the amount of points discriminated winners from losers. Michalopoulou et al. (2005) identified the effectiveness of attack and serve as key predictors for winning teams on the Greek national level.
Similarly, in women's competition, seven factors were found contributing to winning in league rounds, while six factors were contributing to winning in knockout rounds.
Although not similar to men, women teams also showed one factor less contributing during the knockout rounds than league rounds. The differences in the factors between men and women for winning league or knockout may be explained by the fact that males are significantly different from females with respect to physical, physiological, psychological aspects (Lewis, Kamon, & Hodgson, 1986). Previous studies observed differences in the type of techniques used between gender (Koch & Tilp, 2009b;Yiannis, 2008). Women's beach volleyball is considered to employ more effective defense strategies, due in part to their lower levels of strength, speed, and jump height and causes their attacks to not to be as dynamic as in men's volleyball (Macial et al., 2009). A previous study also observed significant sex differences in frequencies of techniques applied for service, reception, setting, attack, and block and defense, which may indicate differences in movement pattern between men and women (Koch & Tilp, 2009b).

Conclusion
Our study concludes that there is a significant association of important factors with respect to winning a match in an elite beach volleyball championship. The coaches and players can take note of the important factors responsible for winning in the elite beach volleyball championship, with different factors playing important role in men and women