Probability and uncertainty are important factors in the engineering decision-making process, and engineers need to be able to make optimized decisions based on given information and subjective interpretations. This differs from the scientific approach in that engineering interpretations are subject to personal experience and opinion.
The most important skill required of an engineer is the ability to make judgments in a given situation. The process of making judgments in the problems they face is called decision-making, and it can range from simply determining the amount of formwork for a concrete pour to determining the location of a port or a developing city. In this process, engineers must have the ability to predict the outcome of several possible alternatives to solve the problem at hand, and to maximize profit. In most engineering problems, decision-making focuses on minimizing the risk that the predicted outcome will differ from the actual outcome.
In real-world engineering practice, decisions are made in the presence of uncertainty about the predicted outcome and, in many cases, with less than perfect information about a given situation. For example, most civil engineers are aware that two different samples obtained from concrete mixed within the same batch will have different strengths. This is because the size, density, proportion of aggregates, cement and water content, and other factors that determine concrete strength are different in the two samples. Therefore, it is unrealistic to expect the durability or load capacity of a completed building or facility to be the same as the design. As you can see, most engineering decisions involve uncertainty.
While scientists view probability simply in terms of the frequency of natural phenomena, engineers faced with decision-making can understand it as a degree of confidence. For scientists, a 0.1 probability of a magnitude 5 or greater earthquake simply means that 10% of all future earthquakes will be magnitude 5 or greater. The important point here is that from a scientific perspective, the probability of an earthquake occurring doesn’t depend on who the scientist is. However, from an engineering perspective, the probability may change. This is because engineering interpretations take into account an engineer’s personal views, experience, and the conditions that can affect an event. So, in engineering terms, a 0.1 probability of an earthquake is the result of a particular engineer’s judgment, and the probability can change as new information is added or as the engineer’s knowledge improves.
Why do we deal with such subjective probabilities in engineering? First, there is a lack of objective information that can influence the outcome, so subjective interpretation is inevitable in the decision-making process. Second, the increasing amount of information available through many investigations means that engineering judgment is moving in a direction that is consistent with scientific judgment. Finally, the application of scientific probability to engineering is inherently unrealistic. For example, in the problem of predicting the depth of an underground bedrock layer, in real-world civil engineering, the depth of the bedrock layer is predicted by drilling a few boreholes at a construction site. Scientific probability is meaningless because it is not feasible in terms of cost and time to dig up soil from every construction site and measure the depth of the bedrock layer.
In conclusion, engineering decision-making is the process of obtaining the optimal information to solve a problem within the available capital. More information available means more money for data research and analysis. Since it is impossible to eliminate all uncertainty, the best option is to predict the optimized outcome at the least cost. Therefore, the idea of reducing risk by understanding uncertainty in engineering problems as scientific probability is misleading. Therefore, research is needed on how to encompass the engineering meaning of the word reliability.
