We used tree diagrams as an illustration of the categories and levels of Tierney’s classification of reasons. Similarly, writers sometimes integrate graphics to make their classification easy for readers to see at a glance.

Here is an example in which Sharon Begley and Martha Brant explain the abuse of performance-enhancing drugs by Olympic athletes, classifying the drugs into five categories:

If doping is, as [the head of IOC’s Medical Commission Prince Alexandre] de Merode noticed, suddenly “an important problem,” it is partly because the newest doping agents pose the risk of serious health problems, and even death. But the larger reason is that it is ridiculously easy to dope and not get caught. Doping and detection are like an arms race. First, trainers discover a performance-enhancing drug. Then, sports officials develop a test for it. Trainers retaliate by inventing a way to elude the detectors. So far, doping has stayed a lap ahead. “Undetectable drugs are 90 percent of estimated doping cases,” says Hein Verbruggen, head of international cycling.

Czech tennis pro Petr Korda tested positive for the steroid nandrolone after the Wimbledon quarterfinals last May, for instance. (Protesting that he did not know how the chemicals got into his system, he avoided the one-year suspension the International Tennis Association is supposed to impose.) But American pro Jim Courier charged that steroids are far from the worst abuse in tennis. “EPO is the problem,” Courier told Newsweek. “I have pretty strong suspicions that guys are using it on the tour. I see guys who are out there week in and week out without taking rests. EPO can help you when it’s the fifth set and you’ve been playing for four-and-a-half hours.” Although the endurance-building effects of EPO last for about two weeks, its use can’t be detected in urine at all or in blood for more than a day or so after the athlete stops taking it.

EPO is only one weapon in a pharmaceutical arsenal of performance-enhancing substances flowing through sports. Stimulants like amphetamines, ephedrine and caffeine were the first substances to land on the IOC’s list of banned agents, and they’re still popular. They provide a quick pop of energy, and so are a favorite of sprinters, cyclists and swimmers. They are an ingredient of many asthma medications. Exercise-induced asthma has inexplicably stricken many Olympians, including 60 percent of the U.S. team in 1994, and medical use of stimulant inhalants is allowed. Are stimulants detectable? Sure, if your trainer’s IQ matches his hat size. They clear the urine in hours, so all an athlete has to do is not take them too close to her event. If you’ve been using too soon before your race, there are always “masking agents.” Probenecid, for one, inhibits substances from reaching the urine. And urine tests are all the IOC requires: blood tests, which can detect more substances, are deemed too invasive.

Anabolic steroids, almost all of them derivatives of the hormone testosterone, are the mothers of all doping agents. They build muscles. By most estimates, an athlete can improve strength at least 5 percent by taking steroids either orally or through injection during high-intensity training. Drug-detection machines, such as the high-resolution mass spectrometer used at the Atlanta Games in 1996, can be tuned to detect any synthetic steroid; the Atlanta lab tested for 100 different types. But the Dr. Feelgoods of sport can tinker with the molecular structure of common steroids, so they slip through. “There are 72 banned steroids,” says one American coach who says he developed drug regimes for athletes in Atlanta, “but the testosterone molecule is changeable in millions of ways. All you have to do is make a steroid not on the list.” Or, simply by going cold turkey a few weeks before competition, an athlete can get the muscle-bulking effects without getting caught. If that seems too chancy, athletes can use a diuretic. These drugs, which are also banned, dilute the urine. That makes illicit substances virtually undetectable.

More and more athletes are turning to the source of all steroids: testosterone itself. Natural levels vary, so sports federations and the IOC try to detect doping indirectly. They measure the relative amounts of testosterone and another natural steroid called epitestosterone. In most people, testosterone levels are no more than twice epi levels. But to allow for individual variation, the IOC set the prohibited level at anything over 6 to 1. That means an athlete can dope himself up to, say, five times his normal testosterone levels, and get away with it. How much of an edge would that provide? A male athlete with a typical testosterone/epitestosterone ratio of 1.3 to 1 could boost that to 6 to 1, stay within the IOC limit and improve his performance at least 10 percent. Women, with a natural ratio of 2.5 to 1, could do even better, since they have less testosterone to begin with and so are more sensitive to added amounts. Testosterone can give women beards, deep voices and tough skin. It can make men’s breasts swell and testicles shrivel.

The doping agents of choice today are substances that cannot be detected in urine: EPO and human growth hormone. Even though the performance-enhancing effects of hGH are unproved, many athletes believe it boosts energy. (Athletes dubbed the Atlanta Olympics “The Growth Hormone Games.”) hGH can also cause grotesque skeletal deformations by stimulating abnormal bone growth. EPO, by increasing the production of red blood cells up to tenfold, can turn blood the consistency of yogurt, making it too thick to flow freely. The misuse of EPO has apparently killed at least 18 Dutch and Belgian cyclists since 1987.

— SHARON BEGLEY AND MARTHA BRANT, “The Real Scandal”