NBA球員簽約與績效之關連性研究-資料包絡法之運用

Abstract

摘要 本研究旨在探討優渥複數年合約對球員表現效率影響，研究樣本為1999年至2008年，十個球季以及NBA30支球隊，共135個符合條件之球員。除透過資料包絡分析法（DEA）、等幅擴張性檢定、敏感度分析及Tobit迴歸模型，對NBA球員效率進行探討，並對NBA重要制度進行簡介，以期對國內SBL提出建議。 研究之主要發現如下：ㄧ、球員之整體效率值、純粹技術效率值都非常的高，尤其規模效率的平均值更是高達0.99，顯示籃球職業運動員普遍具有高水平之技術水準。二、由基本敘述統計發現，簽約後的績效平均數效率值都比簽約前之效率值平均數略低。三、Wilcoxon等級檢定發現簽約前、後兩群組之間Z值為負但無達到顯著差異。四、敏感度分析發現產出變數的總得分與投入變數的罰球次數為關鍵因素。投入變數對效率值的影響，明顯大於產出變數。五、透過Tobit迴歸找出影響球員效率的因子。其中跟效率值有顯著正相關的因素有：先發與否、薪資、球隊勝率。與效率值有顯著負相關的因素是球員年資、簽約前後。在球員戰鬥位置上，結果顯示中鋒的效率值最佳，而前鋒效率值明顯偏低。簽約前後與球員效率值達顯著負相關，方向上與Wilcoxon等級檢定結果相同，由此顯示球員的確會在簽約前努力提升個人績效，而在簽約後，績效下滑，產生道德危險。

Abstract The research is aimed to investigate whether a multiyear contract has an effect on a player's efficiency performance. 135 players are selected from 30 NBA teams during ten seasons, from 1999 to 2008. Data Envelopment Analysis (DEA), Sensitive analysis, and Tobit are used to study the player's performance. The system of the NBA multiyear contract is also introduced in the research. It is expected to give some advice to SBL in Taiwan. The results are indicated as below. (1) the mean of Scale Technical Efficiency (SE) of the NBA player reaches to 0.99. It reveals that professional basketball players, in general, have above-average skills. (2) Based on descriptive statistics, after a player signs the contract, the mean of player’s Efficiency is lower. (3) According to Wilcoxon signed ranks test, Z value between before and after the contract signing is negative, but it is not significant. (4) From Sensitive analysis it shows that a player's points (the output item) and his free throw attempts (the input item) are the key factors. The output item has a bigger effect than the input item. (5) Tobit regression is applied to find out the factors that influence the player's performance. Game started or not, salary, and a team's win-loss percentage have a positive association with a player's efficiency performance. However, seniority and the period of renewing the contract have a negative association. This result corresponds to Wilcoxon signed ranks test. A Center's efficiency performance is the highest while a Forward's is definitely the lowest. In conclusion, a player indeed tries to reach his maximum performance before signing a multiyear contract. Nevertheless, after a player signs the contract, it is a question whether he deserves the salary.