The protocol of this observational study was approved by the Ethics Committee of the Nixus Foundation (Permit Number: 2015–08). Informed consent was not required but sanctioned subjects’ were de-identified prior to analysis.
The 2009 World Anti-Doping Agency Code (World Antidoping Agency 2015) defines ‘doping’ as the occurrence of one or more of the anti-doping rule violations, such as: (1) presence of a ‘prohibited substance’, or its metabolites or markers in an athlete’s sample; (2) use or attempted use by an athlete of a ‘prohibited substance’ or a ‘prohibited method’; (3) refusing or failing without compelling justification to submit to sample collection; (4) violation of applicable requirements regarding athlete availability for ‘out-of-competition’ testing; (5) tampering or attempted tampering with any part of doping control; (6) possession of ‘prohibited substances’ and ‘prohibited methods’; (7) trafficking or attempted trafficking in any ‘prohibited substance’ or ‘prohibited method’; (8) administration or attempted administration to any athlete ‘in-competition’ of any ‘prohibited method’ or ‘prohibited substance’, or administration or attempted administration to any athlete ‘out-of-competition’ of any ‘prohibited method’ or any ‘prohibited substance’ that is prohibited ‘out-of-competition’, or assisting, encouraging, aiding, abetting, covering up or any other type of complicity involving an anti-doping rule violation or any attempted anti-doping rule violation.
The International Tennis Federation has published the complete list of anti-doping offences between 2003 and 2014 (International Tennis Federation 2015). According to the doping definition, all offences to the WADA Code committed by tennis players during that period were collected from the ITF official webpage, registered and analyzed. Data of players’ performance (ranking position, retirement date, etc.) were tracked from the Association of Tennis Professional (ATP) official website (Association of Tennis Professionals 2015).
When the original sanction was modified, usually due to a legal appeal by the player, the final decision was considered for analysis.
The career of professional tennis players is measured by the achievement of ranking positions (Reid et al. 2014). Male professional tennis is a highly competitive sport ranked through an objective, merit-based, mathematical system. Since 1973, the Association of Tennis Professionals publishes weekly lists a 52-week rolling computer ranking points based on tournament category. Therefore, the ranking position is a valid instrument to track tennis players’ performance.
Three ranking positions were determined for analysis: (1) the ranking position at the date of doping sanction (DS-P); (2) the highest ranking position after doping sanction (AD-HP); and, (3) the career highest ranking position (C-HP).
The ATP tour published two different rankings for singles and doubles competitions. For the purpose of this study, sanctioned players were defined as “singles player” or “doubles players” according to their best position in both lists. Players’ retirement date were determined through the last appearance in ATP rankings.
Descriptive statistics were obtained and Chi square tests were performed for comparing data from different groups within samples. Wilcoxon paired test was used for comparison of ordinal variables. P values <0.05 were considered significant. (Statistical package: Statistica for Windows, Statsoft
Tulsa, Oklahoma, USA).