They are the basis for the growing scientific consensus that observed increases in the average temperature of the earth are unlikely to be the consequence of natural variation alone. Similar models can also be used to simulate and evaluate remedial strategies. The mathematical tools of modeling, simulation, and risk analysis validate the cause and effect relationship upon which policy decisions are based, and they permit the evaluation of the effects of alternate courses of action. In addition, chaos theory is providing new lenses through which to view the behavior of such complicated systems. Complex decisions arise in more tangible settings as well, such as choosing among the interrelated options that govern the process of building a complex system like an office building or an aircraft.
Complexity is aggravated by uncertainty.
For example, decisions about dynamic control of traffic in telephone and computer networks are made more difficult by the uncertain patterns of demand. Queuing theory provides guidance for these kinds of decisions. Statistical analysis of clinical trial data guides the Food and Drug Administration's approval of every prescription drug. To ensure an impartial assessment of dose and response effects, drug trials are conducted using protocols dictated by the statistical methodology known as the design of experiments. Assertions about the efficacy of a particular course of treatment are then accompanied by well-defined confidence intervals, statements of the likelihood of treatments being effective in specified circumstances.