18.1.5 Quality Measurement and Six Sigma (6σ)

Intended learning outcomes: Describe the metric of six sigma (6σ) and the sigma conversion table. Identify Six Sigma Quality. Differentiate between three Sigma and Six Sigma process reliability.

Six Sigma (6σ) had its origins in the 1970s in Japan, in shipbuilding and in the electronics and consumer goods industry. In the second half of the 1980s, Six Sigma — pioneered first by Motorola — was introduced as a program to reduce defects in the manufacturing of electronic components. It included a set of methods and techniques focused on quality improvement. Later, the Six Sigma philosophy came to be applied to other business processes for the same purpose, namely, to achieve reliable processes. The aim is to reduce variation and defects in all areas of company performance. Today, Six Sigma is important

• as a metric
• as a problem-solving methodology, or method for improving performance
• as a management system

This section focuses on the first definition.

The term “sigma” is often used as a scale for levels of “goodness” or quality.

Sigma, the eighteenth letter of the Greek alphabet used as a mathematical symbol, was employed for many years by statisticians, mathematicians, and engineers as a unit of measurement for the standard deviation.

Six Sigma (6σ) as a metric is a specific scale for measuring the number of successful products, events, processes, operations, or opportunities.

Figure 18.1.5.1 shows the conversion table for one sigma to six sigma.

Fig. 18.1.5.1       The sigma conversion table.

The conversion table shows an exponential scale, which does not, however, accord with the standard deviation of the normal distribution, as it is often assumed (a glance at the tables in Section 11.3.3 provides easy confirmation of this). Motorola defined the Six Sigma level as equal to 3.4 DPMO. In the world of practice, however the mathematical explanation of the conversion table does not stand at the center of attention.

`Six Sigma Quality is defined as a level of quality that represents no more than 3.4 DPMO (defect parts per million opportunities).`

Figure 18.1.5.2 compares Three Sigma and Six Sigma process reliability, considering examples given by Motorola.

Fig. 18.1.5.2       Three Sigma and Six Sigma process reliability.

Course section 18.1: Subsections and their intended learning outcomes

• 18.1 Quality: Concept and Measurement

Intended learning outcomes: Produce an overview on the quality of processes, products and organizations as well as its measurability. Present the concept of quality measurement and Six Sigma.

• 18.1.1 Process Quality

Intended learning outcomes: Produce an overview on process, service, and a service provided to dependents. Present the characteristics of the quality of processes. Identify process quality, process time, and process load.

• 18.1.2 Product Quality

Intended learning outcomes: Identify product quality. Differentiate between a simple product and a product in a broad sense. Present the characteristics of the quality of products.

• 18.1.3 Organizational Quality — Quality Towards the Stakeholders of an Organization

Intended learning outcomes: Identify organizational quality. Describe the concept of quality toward the stakeholders of an organization.

• 18.1.4 Quality and Its Measurability

Intended learning outcomes: Explain the problems of the measurability of indicators and the step from measurement to corrective actions. Describe the issue using the example of the measurement of customer satisfaction.

• 18.1.5 Quality Measurement and Six Sigma (6σ)

Intended learning outcomes: Describe the metric of six sigma (6σ) and the sigma conversion table. Identify Six Sigma Quality. Differentiate between three Sigma and Six Sigma process reliability.