As with most things we have discussed so far, a clear definition of risk needs to be presented. Risk is often associated with safety however, the two are not synonymous. In a broad sense, safety can be found on physical, psychological, and economic levels. Risk, however, is defined to be a threat to safety. Many of those who have technical training tend to understand risk very narrowly as simply the probability that some given harm will come from a situation. Those who do not have technical training, laypeople, tend to incorporate moral importance into their ideas about risk. Thus, the risk that something bad will happen includes both probability and moral importance. Both perspectives about risk remain incomplete but contain real wisdom. Those with technical training better understand quantitative probabilities, but sometimes ignore the broader aspects of value judgement. Those without technical training better understand how moral importance and personal control enter into a decision, but sometimes confuse attitude with probability.
Engineers often analyze complex automated systems in terms of event trees or fault trees. An analysis using event trees starts by assuming that a particular component will fail, and traces through the consequences of that failure for the entire system. Fault trees trace the process in reverse. The analysis begins with some undesired event at the system level (an airplane crash for example) and traces back to the component failures that could have led to that consequence. While these forms of analysis can prove very useful as systematic aids to assessing risk, they have severe limitations. No one can possibly imagine all the ways a complex system can fail. Furthermore, estimating the probabilities required at each step sometimes proves to be nearly impossible, since the needed data cannot be obtained. Regardless of how risk is perceived, the fact remains that much of what science and technology produce contains risks to human health. This can be seen in the Drug Testing case study. The risks may be inherent in the products themselves, or may arise through the production process.