Posted on: 30th Apr 2020

Types of Reliability in Research


Types of Reliability in Research

Reliability: Definition

Reliability in research can be referred to as a way of analyzing the quality of the measurement process which is utilized for data collection. It can be referred to as a level up to which research methodology generates stable and consistent results.  At the time of performing either qualitative or quantitative research, it is very much important for you to consider the reliability and validity of your study. You to test the reliability of research need to apply similar techniques to similar projects under the same circumstances. If in such cases you get the same outcomes, it represents high reliabilityf of research.

Different types of Reliability

The 4 different types of reliability are:

1. Test-retest

In this method, the researcher performs a similar test over some time. It is a test which the researcher utilizes for measuring consistency in research results if the same examination is performed at different points of time. You can utilize Test-retest reliability for measuring something which you except that will remain stable in the sample.

For example:  A test of color blindness is performed by management in Airlines for testing the issue of color blindness in trainee pilots.  The researcher is expecting that such a study should have high test-retest reliability. As color blindness is a characteristic which will not change with the passage of time.

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  • Importance of test retests reliability

Test-retest reliability is very much essential as many factors can affect results over some time.

For example:  People participating in research may have different moods   which further might have effect on their potential to answer in an accurate manner.

You can use test-retest reliability for assessing the way the Specific method resists different factors over some time. If in case there are only minor variations between two sets of results it represents high test-retest reliability.

  • How to measure it

You need to execute a similar test on the same group of people at different points of time. Only after that, you can compute the correlation between two sets of research results.


Examples of test-retest reliability:  Researcher has a design questionnaire for measuring IQ level of a particular group of people.  The researcher again administers the test after three months apart from the same group.  After analysis, it has been found that there is a great difference, this means that test-retest reliability of Questionnaire design for measuring IQ level is low.

  • Techniques to improve Test-retest reliability

Few techniques which you can utilize for improving test-retest reliability are:

  1. One of the best techniques to improve test-retest reliability is to design such questions in a manner that it should not influence the mood of participants. In simple words, you should prepare a Questionnaire considering the nature of Participants.
  2. At the time of developing a plan for the collection of facts, you should take the initiative for minimizing the effect of external factors. It is also very essential for you to ensure that all samples are tested under similar circumstances.
  3. While creating a plan for conducting research you should expect that changes can take place over some time.

2.. Inter-rater Reliability

It is also known as Interobserver reliability. You can utilize the inter-rater reliability for measuring the level of agreement between several people observing the same thing. You can utilize inter-rater reliability after data collection and at the time when the investigator is assigning ratings to one or more variables.

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Example:  In relation to observational study when data collection related to the behavior of students in the classroom is done by a team of researchers, inter-rater reliability is very much crucial.  It is very much important to have mutual consents between researchers about the technique to be used for categorizing different types of behavior.

  • Importance of inter-rater reliability

All people are subjective, so there could be changes in the perception of the researcher about the behavior of people in different situations. The main purpose of reliable research is to reduce subjectivity so that results can easily replicate the same results.

At the time of designing the scale and selecting criterion for collection of information, it is very crucial to ensure that every person has a rate variable without any biasness.

  • The technique to measure it

The different researcher needs to perform similar observation or measurement on the same sample. After that researcher needs to calculate the correlation between different sets of outcomes.  In case the researcher provides a similar rating it means that the test has high inter-rater reliability.

Example of inter-Rater Reliability: A team of investigators observing the wound healing process in patients. Researchers are using a rating scale for recording the stages of healing. They have set specific criteria for assessing the different aspects of wounds. After completion of the research, a comparison between the results produced by different researchers assessing the same set of patients is done. It has been analyzed that there is a powerful correlation between a different set of results. It means research has high inter-rater reliability.

  • Process of improving inter-rater reliability

The process of improving inters rater reliability include 3 steps these are:

Step 1: At the initial step you need to clearly define different variables of your study. It is also very much important for you to define the research methodology that you will use for measuring it.

Step 2: It is a step where you need to create a detailed and objective criterion based on the determination of how you will rate variables and categorize them.

Step 3: In case there are multiple researchers involved in the study then you need to ensure that all participants have complete information. It is also very crucial for you to make sure that all the participants are provided with proper training.

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3. Parallel form

Researcher design number of versions for testing the reliability of research. It is a type of reliability that helps in measuring the correlation between two equivalent versions of a test.  You can utilize parallel forms of reliability when you have two different assessment tools for measuring similar things.

  • Importance of Parallel form of reliability

In case you want to utilize different versions of the test, for instance, avoiding respondents providing similar answers).  Then you are required to ensure that all sets of Questions provide reliable results.

In the context of educational assessment, it is very much essential for you to create different versions of tests for ensuring that Students Don’t have access to questions.  A parallel form of reliability means in case the same students have two different versions of reading comprehension tests then they should produce the same results in both the tests.

  • How to measure it?

One of the important techniques to measure the parallel form of reliability is to prepare a large set of Questions for evaluating a similar thing. then after that, you need to divide this on random basis into two questions sets

A similar group of respondents answers both sets. and then you need to calculate the correlation between the results. A High correlation between two variables of the study indicates a high parallel form of reliability.

Example of Parallel form of reliability

Research has designed a set of questions for measuring financial risk suffers by [particular group of people. An investigator has a set of questions and respondents are categorizing by applying a random sampling technique.  Then groups are divided into two, fir group I named as A and second group is given name as B.  After that comparison between two tests is done and it has been found that both tests are identical in nature. It represents a highly parallel form of reliability.

  • Techniques to improve the parallel form of reliability

You for ensuring the high parallel form of reliability need to make sure that all questions and tests are based on similar theory and design for measuring similar things.

4. Internal consistency

It includes a single item of the test remains the same. Internal consistency helps in measuring the correlation between different items in a test which intends to measure the same construct.

Researchers can compute internal consistency without having a repetition of the test. It is a good way of assessing reliability when you only have one data set.

  • Importance of internal consistency

When you are devising a set of Questions or ratings which would be integrated into an overall score. It is important to ensure that all of the items do reflect a similar thing. If responses to different items contradict one another.  If responses to various items contradict one another, the test may be unreliable.

You for measuring customer satisfaction with an online store, you can design a questionnaire with a set of statements which respondents should agree or disagree with. Internal consistency tells you whether the statements are all reliable indicators of customers’ satisfaction.

  • How to measure it?

Two common methods which you can utilize for measuring internal consistency are

1. Average inter-item correlation

Researcher design measures for assessing a similar construct, then you can calculate the correlation between the results of all possible pairs of items and then calculate the average.

2. Spilled half reliability

You can randomly split set measures into two sets. After testing the complete set of the respondents. You can compute the correlation between the two sets of responses.

Example of internal consistency

A group of respondents are provided with a set of statements which is design to measure optimistic and pessimistic mindsets.  If the test is internally consistent, an optimistic respondent should generally provide high ratings to optimism indicators and low ratings for permission indicators. Correlation to calculate between all the responses for optimistic statements, but the correlation weak.  This suggests that the test has low internal consistency.

  • Techniques of internal consistency

At the time of devising Questions, which intend to reflect a similar concept which is based on a similar theory. You need to carefully formulate research questions.

Which type of reliability applies to research?

You must consider reliability at the time of planning a research design before starting to collect and analyze data. The type of reliability you need to compute is completely based on the type of research and methodology.

Type of methodology? Type of reliability
If you intend to measure a property that you expect that will remain constant over some time.Test-retest
Number of investigator making observations  on the same topicInter-rater
Utilizing two different tests for measuring similar thingsParallel form
Utilizing a multi-item test where you intend to measure a similar variable.Internal consistency

In addition to this, you can calculate the reliability of research using statistical technique and you can state this along with results.


It has been concluded from the above that the reliability of research is very crucial for generating accurate results. Another fact which has been discovered is that reliability can be measured using Statistical techniques.

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Author Bio:

Angela Wong

Hi Guys, Happy to help you in research paper writing. I am post graduate from SUSS and now involved in providing assistance to Singapore students for making research projects during masters and Phd scholars. You can consult me for marketing, management, finance, accounting or any kind of research paper writing query