Reliability and Validity – Definition, Use & Types

20.08.20 Reliability & Validity Time to read: 8min

How do you like this article?

0 Reviews


Reliability and Validity serve as fundamental methodologies in research, setting the standards for data quality and accuracy. Assigning numerical values to a set of characteristics is necessary to assess somaeone or something. This method generates the data we evaluate. Without these elements, the conclusions drawn from evaluation may be questioned or dismissed, potentially leading to erroneous applications or other types of research bias.

Reliability and Validity – In a Nutshell

  • Researchers use Reliability and validity to evaluate their measures.
  • Reliability is consistency over time, between items, and between researchers.
  • The degree to which the scores accurately reflect the variable they are intended to evaluate is referred to as the validity.
  • A measurement’s validity and reliability are not determined by a single study but by the pattern of results across many studies. The assessment of reliability and validity is a continuous activity.

Definition: Reliability and Validity

Reliability and validity are often considered the two most important qualities of any given measurement instrument or procedure. It’s essential to note that there is no perfect validity or reliability. While it’s possible to think of certain measures as being accurate, the reality is that all measures will contain one or more sources of error. Reliability and validity refer to a method’s capacity to accurately measure something. In other words:

  • Reliability refers to a measure’s consistency
  • Validity relates to a measure’s precision

Difference between Reliability and Validity

The quality of research can be assessed by its reliability and validity. They show the accuracy of a measurement method, a methodology, or a test. Validity refers to the accuracy of a measurement; reliability to its consistency.

Reliability Validity
What does it tell you? The degree in which the same results are obtained when the study is repeated under identical conditions. How accurately the results measure what they're intended to measure.
How is it assessed? Examining the consistency of outcomes over time, between various observers, and within the test itself. Comparing the accuracy of the results to accepted theories and other measurements of the same idea.
How do they relate? Even though a reliable measurement may be repeatable, it's not always accurate. A valid test can be trusted; if a test yields the right outcomes, it should be repeatable.
Conduct a final format revision for a print of your thesis
Before submitting your thesis for print, cheque on your formatting with our 3D preview function for a final time. It provides an exact virtual visualization of what the printed version will resemble, making sure the physical version meets your expectations.

Understanding Reliability and Validity

Reliability and validity are closely connected but have distinct meanings. A measurement can be reliable, but not necessarily valid. However, valid measures are also reliable.

Understanding Reliability

Reliability refers to the consistency with which a method measures a variable. The measurement is considered reliable if the exact result can be attained consistently by employing the same techniques every time under the same conditions.


You conduct a series of temperature measurements on a liquid sample under the same conditions each time. Because the thermometer shows the same temperature every time, the findings may be deemed reliable.

Understanding Validity

Validity refers to the precision with which a method measures the target variable. If a study has high validity, its findings correlate to the actual traits, characteristics, and fluctuations of the physical or social reality. A measurement’s validity may be indicated by its high reliability. If a method cannot be relied on, it is most likely not valid.


If the thermometer displays different temperatures each time, despite carefully controlling the environment to ensure the sample’s temperature remains constant, it is likely faulty, and its results are consequently invalid.

Reliability and validity are two important concepts in research and measurement. Attached you will find a graphic that shows you four possible outcomes. These will be described in more detail later to highlight the difference between the two terms.

  1. Reliable, not valid
    When a measure is reliable but not valid, it means that the instrument or test produces consistent results over time or across different settings, but those results are not an accurate reflection of the construct or variable it is supposed to measure.
  2. Low reliability & validity
    When both reliability and validity are low for a particular measure or test, it means that the tool is neither consistent nor accurate in what it aims to measure. Such an instrument is generally considered to be of poor quality and is unlikely to provide useful or trustworthy data.
  3. Not reliable, not valid
    When a measure is neither reliable nor valid, it represents a significant issue for any research or practical application, as it fails to provide consistent, accurate, or meaningful information. In such a case, the instrument or test neither measures the intend construct accurately (lack of validity) nor yields consistent results across different occasions, settings, or groups of people (lack of reliability).
  4. Reliable & valid
    When a measure is both reliable and valid, it is considered to be a high-quality instrument that can be trusted to provide consistent, accurate data.


Assessing Reliability vs. Validity 

Reliability vs. validity is measured in different ways. By comparing various copies of the exact measurement, one can assess the reliability of the survey items. Validity is more challenging to evaluate, but can be approximated by comparing the findings to relevant facts of hypotheses.

Types of Reliability

Distinct statistical methodologies allow for the estimation of various types of reliability. To certify the reliability of a measurement instrument, employing a wide range of expertise in the subject field and diverse conceptual models is essential. This ensures that the data produced by your tool is coherent with the broader context. Below are the types of reliability and validity:

Type of Reliability Assessment Example
Test-Retest The consistency of measurement across time: Do repeated measures yield the same results? A group of individuals completes a questionnaire meant to assess personality traits. Test-retest reliability is high if individuals retake the questionnaire later and provide the same responses.
Interrater Do different raters come up with the same results when performing the exact measurement? Five examiners provide significantly varied evaluations for the same student's project, each based on a chequelist of evaluation criteria. This suggests that the chequelist's inter-rater reliability is low.
Internal Consistency Do different sections of a test that is designed to assess the same thing consistently yield the same results? You perform a survey to gauge self-esteem. If the findings are randomly split in half, they should be strongly correlated. The dissimilarity between the two outputs suggests a lack of consistency in the system.

Types of Validity

A measurement’s validity can be evaluated using three primary categories of evidence. Each type of validity is valuable using either expert opinion or statistical approaches. To evaluate the legitimacy of a causal link, you must also consider the experiment’s internal validity (the experimental setup) as well as its external validity (the extent to which the findings can be generalized).

Type of Validity Assessment Example

Conformity of measurement to current theory and understanding of the concept being tested. A self-esteem questionnaire could be evaluated by evaluating other attributes known or presumed to be associated with self-esteem. A strong relationship between self-esteem ratings and associated qualities would show high construct validity.
Content The degree to which the measurement encompasses all features of the measured concept. A test designed to assess the Spanish proficiency of a group of pupils includes reading, writing, and speaking but no listening sections. Experts concur that listening is a crucial element of language ability; hence, the assessment lacks content validity for gauging the total Spanish proficiency level.

The degree to which a measurement's results are in line with those of other exact measurements of the same term. A survey is undertaken to determine the political views of a region's voters. If the results accurately anticipate the outcome of a subsequent election in that region, then the poll has a high criterion validity.

Ensuring Reliability vs. Validity

Your results’ reliability vs. validity depend on developing a solid research design, selecting appropriate methodologies and samples, and conducting it with precision and consistency.

Ensuring Reliability

Throughout the process of data collection, ensuring reliability vs. validity must be considered. When collecting data with a tool or method, the results must be accurate, consistent, and repeatable. Here are some tips to ensure reliability.

  • Apply Your Methods Consistently
  • Standardize the Research Conditions

Ensuring Validity

An accurate assessment of differences can only be made when ratings that accurately reflect the variations are used. Validity should be considered early in the research process when deciding how to collect data. Below you’ll find some tips:

  • Choose Appropriate Methods of Measurement
  • Utilize the Correct sampling techniques

Incorporating Reliability vs. Validity

Discussing reliability vs. validity in various portions of your thesis, dissertation, or academic paper is appropriate. Your work is more reliable and trustworthy if you demonstrate that you considered them when arranging your research and evaluating the results.

litreature ReviewOther researchers have made what efforts to develop and enhance reliability vs. validity research methods?

Methodology – How did you design your study to ensure the reliability vs. validity of the instruments used? This includes the number of samples, environmental conditions, sample preparation, and measurement methodologies as well.

Results – Include these numbers with your primary findings if you have calculated reliability vs. validity.

Discussion – Now is the time to discuss the reliability vs. validity of your results. Were they consistent and reflective of genuine values? If not, then why?

ConclusionIf the findings’ reliability vs. validity were a significant issue, it would be helpful to highlight this right here.

Where to write about Validity and Reliability

Researchers need to confer reliability and validity on different parts of their dissertation or thesis statement. They need to show that they accounted for them when planning the research. The same must be done when interpreting the results. It helps to make the project more trustworthy and credible.

Reliability and Validity in Your Thesis

In a thesis, reliability is typically ensured by using consistent and standardized methods for data collection and analysis, enabling future researchers to replicate the study and arrive at similar conclusions. Validity is achieved by carefully designing the research to accurately measure what it is intended to measure, often validated through pilot testing and by comparing results to existing academic litreature.

Section What to Discuss
litreature Review Here, you need to discuss what other people in this field have done to improve or devise valid and reliable methods.
Methodology State how you planned the research process to guarantee the reliability and validity of all measures employed. Make sure to note the sample set, preparation, measuring techniques, and external conditions.
Results In case you get to calculate reliability and validity, ensure these values are stated together with the results attained.
Discussion Use this section to discuss what makes your results reliable and valid. Ensure you comment on whether the results you attained were consistent and if you were able to reflect the correct values.
Conclusion If you had a hard time proving the reliability and validity of your results, make sure to note that in this section.
cheque your final paper for plagiarism
Not properly attributing credit to original sources often causes deductions in marks. Use our online plagiarism chequeer to reduce the risk of such penalties and correct any potential plagiarized passages. It takes only 10 minutes to submit your paper confidently.


Validity aims to tell you whether a test is suitable for a situation you may have in mind. Reliability, on the other hand, seeks to inform you whether a score attained on the same test is trustworthy or not. In short, you can’t draw a valid conclusion from any test score without being certain about the reliability of the test.
Just because a test is deemed reliable doesn’t imply that it’s going to be valid. So, does reliability affect validity? YES, it does!

The main difference between reliability and validity lies in what each term means or refers to:
Reliability implies the limits to which a particular tool used in the assessment process can yield constant results, even after taking repeated measurements.
On the other hand, validity is used to discuss the degree to which the research instrument will get to measure the objects or items the student researcher has in mind.

Validity, unlike reliability, is based on judgment. It’s a level to which your attained test scores can truly represent their intended variables. What this means is that reliability is consistent across researchers, across items, and across time.

As earlier mentioned, it’s possible for a test to be reliable, implying that all those taking the test are likely to get a similar score regardless of where or when they sit for it (but within reason). However, this isn’t to imply that the test is capable of measuring what it seeks to measure or even that it’s valid. Therefore, the test can be reliable but, at the same time, remain invalid.

Validity is more difficult to evaluate than reliability; however, it’s more crucial. To acquire usable results, you must collect data using valid methodologies; the research must measure what it purports to measure. This ensures the validity of your data analysis and findings.