Reliability Engineering: Definition & Purpose

Instructor: Olu Adesida

Olu has a Master of Science degree in Business Information Technology.

In this lesson, you will be learn about reliability engineering. You will also learn about it's objectives, how it is implemented and how it can be measured.

Reliability Engineering Defined

Reliability engineering is engineering that emphasizes dependability in the life-cycle management of a product. Reliability is defined as the ability of a product or system to perform its required functions without failure for a specified time period and when used under specified conditions. Engineering and analysis techniques are used to improve the reliability or dependability of a product or system.

Reliability engineering falls within the maintenance phase of the software development life cycle (SDLC). The overall aim of the SDLC is to make software and products more reliable.

Reliability Engineering Objectives

The main objectives of reliability engineering are:

  • To apply engineering knowledge and specialist techniques to prevent or to reduce the likelihood or frequency of failures
  • To identify and correct the causes of failures that occur despite the efforts to prevent them
  • To determine ways of coping with failures that occur, if their causes have not been fixed
  • To apply methods for estimating the likely reliability of new software and for analyzing reliability data


Reliability can be difficult to specify, since it is defined in qualitative terms. Reliability is a prediction of the performance of a system or product in the future. It is usually defined as the probability that a product will operate without failure for a stated number of transactions over a stated period of time. Reliability metrics are stated as probability statements that are measurable by testing.

Examples of reliability requirements specifications are as follows:

  • A patient monitoring system can fail less than 1 hour per year.
  • The software shall have no more than x number of bugs per 1000 lines of code.


The justification of reliability engineering hinges on the question: 'What is the cost of achieving reliability goals and the risk of not doing so?'

Testing is the main implementation mechanism which can be used to determine the reliability of a system or product. Thorough testing, combined with the data it generates, product reliability predictions can be made. The measure of reliability is determined based on the trade-off between increased in levels of reliability and increased levels of testing.

It important to note that failing tests prove the absence of reliability.


There are various ways to measure the reliability of a product or software:

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