Difference between validity and reliability

Difference between validity and reliability

Simply, the validity of the measuring instrument represents the degree to which the scale measures what is expected to be measured. Not the same as reliability, which refers to the degree to which measurement produces consistent results.

For the purposes of verifying the accuracy and applicability, it is necessary to evaluate a multi-element measurement scale, in terms of reliability, validity and generalizability. These are some preferred qualities that measure the goodness in the measurement of the characteristics considered. The validity is all relative to the genuineness of the research, while the reliability is nothing other than the repeatability of the results. This article will analyze the fundamental differences between validity and reliability.

Comparative graph

Basis for comparisonValiditAffidability
Sense Validity implies the extent to which the research tool measures, what one intends to measure. Reliability refers to the degree to which the scale produces consistent results when repeated measurements are taken.
Tool A valid and always reliable tool. A reliable tool does not have to be a valid tool.
Related to Precision Precision
Value Of Pi Comparatively less.
Rating Difficult Easy

Definition of validity

In statistics, the term validity implies utility. the most important meter that indicates the degree to which the research tool measures, what is supposed to measure.

Simply, it measures the point where the differences discovered with the scale reflect the true differences, among the objects on the features in the studio, instead of a systematic and random error. To be considered perfectly valid, it should not have any measurement errors. There are three types of validity, which are:

  • Validity of the content : otherwise known as face validity, the point at which the scale provides adequate coverage of the subject being tested.
  • Validity of the criterion : the type of validity that measures the performance of the measuring instrument, or if it behaves as expected or estimated, with respect to the other variables, chosen as a significant parameter. The criterion should be relevant, impartial, reliable, etc.
  • Build validity : Build validity in one measure refers to the extent to which it adheres to the correlations estimated with other theoretical assumptions. Includes:
    1. Convergent validity
    2. Valid discriminating
    3. Nomological validity

Definition of reliability

Reliability means the extent to which the measuring instrument provides consistent results if the measurement is repeatedly performed. To assess the reliability approaches used are test-tests, internal consistency methods and alternative forms. There are two key aspects that need to be indicated separately are:

  • stability : the degree of stability can be verified by comparing the results of repeated measurements.
  • Equivalence : equivalence can be assessed when two researchers compare the observations of the same events.

Systematic errors do not affect reliability, but random errors lead to inconsistency of results, therefore to a lower reliability. When the research tool conforms to reliability, then you can be sure that the temporary and situational factors do not interfere. Reliability can be improved through:

  • The standardization of the conditions in which the measurement occurs, that is the source through which the variation takes place, must be removed or reduced to a minimum.
  • Carefully design the measurement indications by employing people with experience and motivation, for research and also by increasing the number of samples to be tested.

Key differences between validity and reliability

The points presented below explain the fundamental differences between validity and reliability:

  1. The degree to which the scale measures, what designed to measure, known as validity. On the other hand, reliability refers to the degree of reproducibility of results, if repeated measurements are performed.
  2. When it comes to the instrument, a valid instrument always reliable, but the opposite is not true, that is, a reliable tool does not necessarily have to be a valid instrument.
  3. While evaluating the multi-item scale, the validity is considered more valuable than reliability.
  4. The reliability of the measuring instrument can easily be assessed, however, to assess the difficult validity.
  5. Validity focuses on precision, which controls whether the balance produces expected results or not. On the contrary, reliability focuses on precision, which measures the extent to which the scale produces consistent outcomes.


To sum up, validity and reliability are two fundamental tests for sound measurement. The reliability of the instrument can be assessed by identifying the proportion of systematic variation in the instrument. On the other hand, the validity of the instrument is evaluated by determining the degree to which the variation in the score of the observed scale indicates the actual variation between those tested.