The misconceptions and vagueness of the popular views do not help the quality improvement effort in the industries. To that end, quality must be described in a workable definition. Crosby (1979) defines quality as "conformance to requirements" and Juran and Gryna (1970) define it as "fitness for use." These two definitions are related and consistent, as we will see later. These definitions of quality have been adopted and used by many quality professionals.
"Conformance to requirements" implies that requirements must be clearly stated such that they cannot be misunderstood. Then, in the development and production process, measurements are taken regularly to determine conformance to those requirements. The nonconformances are regarded as defects ”the absence of quality. For example, one requirement (specification) for a certain radio may be that it must be able to receive certain frequencies more than 30 miles away from the source of broadcast. If the radio fails to do so, then it does not meet the quality requirements and should be rejected. By the same token, if a Cadillac conforms to all the requirements of a Cadillac, then it is a quality car. If a Chevrolet conforms to all the requirements of a Chevrolet, then it is also a quality car. The two cars may be very different in style, performance, and economy. But if both measure up to the standards set for them, then both are quality cars .
The "fitness for use" definition takes customers' requirements and expectations into account, which involve whether the products or services fit their uses. Since different customers may use the products in different ways, it means that products must possess multiple elements of fitness for use. According to Juran, each of these elements is a quality characteristic and all of them can be classified into categories known as parameters for fitness for use. The two most important parameters are quality of design and quality of conformance.
Quality of design in popular terminology is known as grades or models, which are related to the spectrum of purchasing power. The differences between grades are the result of intended or designed differences. Using the example of cars again, all automobiles provide to the user the service of transportation. However, models differ in size , comfort , performance, style, economy, and status. In contrast, quality of conformance is the extent to which the product conforms to the intent of the design. In other words, quality of design can be regarded as the determination of requirements and specifications and quality of conformance is conformance to requirements.
The two definitions of quality (conformance to requirements and fitness for use), therefore, are essentially similar. The difference is that the fitness for use concept implies a more significant role for customers' requirements and expectations.
1.2.1 The Role of the Customer
The role of the customer, as it relates to quality, can never be overstated. From a customer's standpoint, quality is the customer's perceived value of the product he or she purchased, based on a variety of variables such as price, performance, reliability, and satisfaction. In Guaspari's book I Know It When I See It (1985 p.77), he discusses quality in the customers' context as follows :
Your customers are in a perfect position to tell you about quality, because that's all they're really buying. They're not buying a product. They're buying your assurances that their expectations for that product will be met.
And you haven't really got anything else to sell them but those assurances. You haven't really got anything else to sell but quality.
From a concept's high-level definition to a product's operational definition, many steps are involved, each of which may be vulnerable to shortcomings. For example, to achieve the state of conformance to requirements, the customers' requirements must be first gathered and analyzed , specifications to meet those requirements must be produced, and the product must be developed and manufactured accordingly . In each phase of the process, errors can occur that will affect the quality of the finished product. The requirements may be erroneous (this is especially the case for software development), the development and manufacturing process may be subject to variables that induce defects, and so forth. From the customer's perspective, satisfaction after the purchase of the product is the ultimate validation that the product conforms to requirements and is fit to use. From the producer's perspective, once requirements are specified, developing and producing the product in accordance with the specifications is the path to achieving quality. Usually, for product quality, the lack of defects and good reliability are the most basic measures.
Because of the two perspectives on quality (customer satisfaction as the ultimate validation of quality and producer's adherence to requirements to achieve quality), the de facto definition of quality consists of two levels. The first is the intrinsic product quality, often operationally limited to the product's defect rate and reliability. This narrow definition is referred to as the "small q " ( q for quality). The broader definition of quality includes product quality, process quality, and customer satisfaction, and it is referred to as the "big Q ." This two-level approach to the definition of quality is being used in many industries, including the automobile industry, the computer industry (both software and hardware), and the consumer electronics industry.
The two-level concept of quality is supposed to form a closed-loop cycle: customer's wants and needs requirements and specifications products designed, developed, and manufactured in accordance with the requirements, and with continuous focus on process improvement excellent product quality, plus good distribution and service processes total customer satisfaction. However, this was not always the case in many industries, especially before the late 1980s when the modern quality era began . Product requirements were often generated without customer input, and customer satisfaction was not always a factor in business decision making. Although the final products conformed to requirements, they may not have been what the customers wanted. Therefore, the customers' role should be explicitly stated in the definition of quality: conformance to customers' requirements.
What Is Software Quality?
Software Development Process Models
Fundamentals of Measurement Theory
Software Quality Metrics Overview
Applying the Seven Basic Quality Tools in Software Development
Defect Removal Effectiveness
The Rayleigh Model
Exponential Distribution and Reliability Growth Models
Quality Management Models
In-Process Metrics for Software Testing
Complexity Metrics and Models
Metrics and Lessons Learned for Object-Oriented Projects
Measuring and Analyzing Customer Satisfaction
Conducting In-Process Quality Assessments
Conducting Software Project Assessments
Dos and Donts of Software Process Improvement
Using Function Point Metrics to Measure Software Process Improvements
A Project Assessment Questionnaire