Q 458. Explore different definitions of Reliability. Does it have different meanings based on Industry or Domain? What are the common components of Reliability in most/all definitions?

 

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Reliable ( adjective) - Meaning as per Oxford-learners Dictionary 

 

1.      that can be trusted to do something well; that you can rely on

 Example – A reliable, dependable friend , companion

2.     that is likely to be correct or true.

Example : reliable information/data

3.      able to work or operate for long periods without breaking down or needing attention

Example : My car's not as reliable as it used to be.

Reference : https://www.oxfordlearnersdictionaries.com/definition/english/reliable

 

Similarly Reliability is noun of above term

Reference : https://www.oxfordlearnersdictionaries.com/definition/english/reliability?q=reliability

 

 

Definition -2 is widely used in statistics, whereas Definition – 3  is predominant in industrial / service sector on defining, measuring, controlling machine , equipment , device, accessory performance.

 

Statistical relevance, example of performing a analytical test by Chemist in Laboratory :

• Inter-rater: Different Chemists, same test.
• Test-retest: Same Chemist, different times.
• Parallel-forms: Different Chemists, same time, different test.
• Internal consistency: Different questions / parameters, same construct / test.

Above definitions are some thing similar to Gage R&R falling under Measurement Systems Analysis, where these are also defined as Repeatability, Reproducibility, Accuracy. Based on these data, conclusions are drawn whether a testing method is robust to adopt or not. In laboratory testing method development, this is one of the most important aspect which one looks at in approving test methods and also supporting regulatory requirements.

 

Coming to Equipment / machine reliability – as explained earlier this definition is widely used in industrial setting. The famous Total Productive Maintenance ( TPM) which is a robust management practice is actually centered around Asset/ Equipment/machine reliability. Here are the few following terms come in to play in defining Reliability.

 

• Breakdowns ( an unplanned event of stoppage)
• Errors ( a deviation from standard)
• Compliance to standard
• Performance – actual vs standard
• Over-all Equipment Effectiveness
• Mean time between Failure
• Mean time to repair

 

Conclusion : Term “ Reliability “ is extremely important parameter / metric not only as a qualitative attribute , bust also powerful SMART metric in defining, measuring, monitoring , controlling and improving performance ( of test, equipment /device)

The dictionary meaning of ‘Reliability’ says ‘The Quality of being Trustworthy or Performing consistently well'. It is also defined as the degree to which the result of a measurement, calculation or specification can be depended on to be accurate.

 

Reliability as ‘Trust’

As a layman, the term ‘Reliability’ is often used with a connotation of ‘Trust’. We may say that this brand is reliable, or this person is reliable, this bank is reliable, this doctor is reliable etc. It means the we can trust and proceed on any association with these entities.

 

Reliability as 'Accuracy'

If the term reliability is used with respect to an information, measurement or calculation, it implies accuracy.

 

Reliability as a product performance

In case of manufactured products, ‘Reliability’ is the ability of a product to perform a required function under stated conditions for a stated period of time.

In simpler terms, the reliability is the probability that a product will be ‘failure-free’ for a stated period of time or beyond.

The probability of failure is usually based on the percentage of ‘survivors’ out of a large number of products.

 

Reliability metrices

The reliability of an equipment is also expressed in terms of ‘Mean Time Between Failures’ (MTBF) for repairable items. If the item is not repairable, ‘Meant Time To Fail’ (MTTF) is applicable.

Mathematically, Reliability is expressed as the Probability of Survival

R = P(S) = e ^-t/µ

Where t = specified period of failure free performance; µ = MTBF.

 

Reliability of Service

In the context of a service industry, ‘Reliability’ is the probability of the agreed level of service within a specified time (for example, a courier service).  However for certain types of services, safety also matters. (for example, a cab service).

 

Reliability as a Commitment

The term ‘Reliability is also used to express the level of fulfilment of a commitment. For example, we book a hotel room based on the features and pictures depicted in an online advertisement. After checking in, if we feel that the extent and quality of facilities provided are not up to the projected levels, we may feel deceived and say that this hotel is ‘not reliable’.

 

Though we discussed multiple contexts, one of the common components about reliability is the factor or Trust, (or not being let down against expectations), be it a Product, a Service or a Commitment.

Definitions of Reliability

 

Manufacturing & Service

-       Change of Quality over time.

-       The ability of a product, service, or system to maintain the original level of quality over time and under different conditions.

-       The probability that is inherent in a system, service, or product that ensures it effectively carries out it’s designed function over a specified time, in a defined environment without failure.

 

Research

-       Reliability is the consistency of a research study or measuring test. https://www.simplypsychology.org/reliability.html).

-       Reliability is the consistent replication of findings from research.  A high correlation coefficient indicates high reliability.

 

Psychometrics/Statistics

-       The overall consistency of a measure. A highly reliable measure repeatedly produces similar results under similar conditions.

-       "It is the characteristic of a set of test scores that relates to the amount of random error from the measurement process that might be embedded in the scores” https://en.wikipedia.org/wiki/Reliability_(statistics)

 

Components of Reliability

 

Manufacturing & Service

• These are the likelihood of success, the designed function, performance within given specification limits, a time period, and the environment/conditions such as the temperature, speed, or pressure.
• ASQ defines these elements as the probability of success, durability, dependability, quality over time, and availability to perform the function.

 

Psychometry/Statistics.

• The components of reliability are precision, reproducibility, and consistency.
• Measurements are influenced by factors that contribute to consistency and factors that contribute to inconsistency.
• The factors that contribute to consistency are the stable characteristic of the person or the attribute that is being measured whereas the factors that contribute to inconsistency are attributes of the person or circumstance that might alter the measurement. Examples of these are things such as health, tiredness, motivation, emotions, comprehension of the task, attention, distractions, instructions, and even luck.

Four Main Types of Reliability

• Test-retest. This is conducting the same test over a period of time.
• Interrater Reliability. This is conducting the same test but by different individuals
• Parallel Forms Reliability. This is conducting alternate versions of tests that are designed to measure the same attribute.
• Internal Consistency Reliability. This is the correlation between multiple items of the test and the construct it is supposed to measure.

Examples of Reliability

• Electric Scooter under a warranty of 24,000 Kms or 2 years whichever is earlier
• Television. Life time guarantee.
• Ecommerce website uptime is 99.997%
• Once data entry error per one million keystrokes

References

https://asq.org/quality-resources/reliability

https://www.simplypsychology.org/reliability.html

https://en.wikipedia.org/wiki/Reliability_(statistics)

https://www.scribbr.com/methodology/types-of-reliability/

The winner for this question is Johanan Collins. Prabhu's response is also quite good. Do read the Benchmark Six Sigma Expert view by Mr. Venugopal R