Just read the "GRE General Practice Book" sent to me by ETS. The Argument Task is totally different from my prospective. The sample topic states:
Hospital statistics regarding people who go to the emergency room after roller skating accidents indicate the need for more protective equipment. Within this group of people, 75 percent of those who had accidents in streets or parking lots were not wearing any protective clothing (helmets, knee pads, etc.) or any light-reflecting material (clip-on lights, glow-in-the-dark wrist pads, etc.). Clearly, these statistics indicate that by investing in high-quality skaters will greatly reduce their risk of being severaly injured in an accident.
In my opinion, the most significant flaw in this argument is that it does not take into account of the ratio of people who wearing equipment to those who do not. Say, for example, 95 percent people do not wear protective equipment while only 5 precentage do. According the the statistics, the risk among those who wear equipemnt will be higher than those who do not.
However, none of the analyses care about this point. Without this vital point, I think all other very detailed analysis as given by ETS worth nothing.