Athletes have historically been willing to take legal and health risks to improve their performance, with some even stating their willingness to risk their lives, as exemplified by research by Mirkin, Goldman and Connor in researching attitudes to the so-called Goldman dilemma. To prevent use of performance-enhancing substances, athletes must submit to drug tests that are conducted both in and out of competition by anti-doping officials or accredited medical staff. Penalized athletes are susceptible to higher testing upon return to competition. Athletes found to have taken substances on the World Anti-Doping Agency's banned list receive sanctions and may be banned from competition for a period of time that corresponds to the seriousness of the infraction. However, the use of substances not on the prohibited list may also result in sanctions if the substance is deemed similar to a banned substance in either composition or effect. Athletes may also be sanctioned for missing tests, seeking to avoid testing or tampering with results, refusing to submit to testing, through circumstantial evidence, or confession of use.