3.9.1. Ishikawa Diagram

The Ishikawa diagram is also known as a cause–effect diagram, fishbone diagram, or root cause analysis diagram, and was developed by Kaoru Ishikawa in the 1960s [63,64]. It helps to visualize a problem and categorize its root causes; it is considered as one of the seven basic quality management tools. The head of the diagram lists the problem to be studied, whereas the fish bones are arrows connected to the spine that list the causes that contribute to the problem. The arrows are interpreted as causal relationships.

According to Da Fonseca et al. [65], the diagram ramifications represent the possible sources of the problem that are related to some factors, such as materials work methods, workforce, measurements, machinery/equipment, and environment. The Ishikawa diagram offers multiple advantages, among which the following can be highlighted [66]. It:


In this case study, an Ishikawa diagram is designed to find the root causes of the problem. For instance, it is supposed that there is an absenteeism problem in a manufacturing company; therefore, managers want to know the different causes of this problem that are related to the factors previously mentioned. Once the causes of the problem are identified, they are categorized by their factors, as shown in Figure 3.

**Figure 3.** Ishikawa diagram to illustrate the causes of an absenteeism problem.

#### 3.9.2. Pareto Chart

The Pareto chart is a special type of bar graph in which each bar represents a different category or part of a problem [67]. It was developed by the Italian scientist Wilfredo Pareto, who found that 80% of the wealth was held by 20% of the people in Italy [68]. The Pareto chart illustrates the frequency distribution of descriptive data that are classified into categories. The categories are placed on the horizontal axis, whereas the frequencies are placed on the vertical axis [67,68]. The categories are arranged in a descending order, from left to right, while a line represents the frequencies in cumulative percentage. The highest bars of the chart represent the categories that contribute the most to the problem.

Furthermore, Pareto charts help identify how certain factors influence on a problem along with other factors; in other words, Pareto charts help identify the best opportunities for improvement [69]. Experts recommend using Pareto charts for two particular purposes: to decompose a problem into categories or factors and to identify the key categories that contribute the most to a specific problem [67]. For instance, continuing with the example of absenteeism in a manufacturing company, the six causes shown in Figure 3 were ordered according to their frequencies, as shown in Figure 4. Based on this order, managers should try to eliminate the first three causes (extreme temperature, sharp tools, and workload), since they represent the 80.47% of all causes of absenteeism.

**Figure 4.** Example of a Pareto chart application for causes of absenteeism.

In the present case study, a Pareto chart is created for a better understanding of the key causes that contribute to the problem of non-working custom cable assemblies.
