Posted on: 29th Apr 2020

Difference between Internal and External Validity

Both internal validity and external validity are very much important in research.  Without internal and external validity research has no meaning.

Difference between Internal and External Validityv

Internal Validity: Meaning

Internal validity helps in measuring the effectiveness of research. The main purpose of internal validity is to analyze the effectiveness of research.  It is a degree up to which a piece of evidence which supports a claim about the relationship between cause and effect. The researcher utilizes internal validity as a technique for measuring accuracy.  It helps in determining whether it is an independent variable which influences the dependent variable

Internal validity helps the researcher in giving an alternative explanation for research results.  You can increase the internal validity of research by including fewer confounding variables.

External Validity: Meaning

 External validity refers to as extend up to which you can apply conclusions of the scientific research in other fields of study. In simple words external validity is a level up to which research results can be generalized across different situations and times.  It helps the researcher in determining whether research Finding is accurate or not. You can measure the accuracy of research findings by performing an examination of its applicability in different circumstances. In case a particular set of research conditions does not practically consider the interaction of other variables of the real world.  The two common types of external validity which help in measuring the strengths of research are:

  • Population validity
  • Ecological validity

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Comparison  between Internal Validity Vs External Validity

The little difference between internal and external validity is that internal validity mainly emphasizes on the relationship between different variables of the study. On the other hand, external validity mainly emphasizes on Universal applicability of research results.

Other differences between internal and external validity are:

Basis of Comparison Internal ValidityExternal validity
MeaningInternal validity can be referred to as level up to which an experiment is free from mistakes. Differences in measurement might arise because of the independent variable.External validity is a degree up to which research results could apply to a real-world situation.
Concerned withControllingNaturalness
MeasureInternal validity helps in measuring the accuracy of the experiment.External validity helps in determining causal relationship which is observed in the experiment can be generalized.


It helps in determining the powerfulness of research methods.  The main aim of external validity is to identify whether research results can apply in the real world.
DescriptionExtend up to which the conclusion is warranted. Level up to which the investigation is warranted for generalization of result to other contexts.
Used toInternal validity is helpful in the elimination of alternative explanations for research results.A generalization of results.
Techniques to improve The best technique to increase internal validity is to include fewer confounding variables in research.An appropriate technique for improving external validity is to include participants in research planning and inform them about objectives.
ThreatsThreats to internal validity are :

a) Confounding factors: Unexpected factors that can affect the relationship between variables which is already been tested.

b) Maturation: It is the changes in the situation with passage of time which can influence the dependent variables of the study.

c) Testing: Pre-testing affect the outcomes of post-test,

d) Participant Selection:  It means the difference in the experimental and control groups can have a great influence on the internal validity of the research.

e) Mortality:  Participants may leave the research.  The main reason for drop out of participants from the study is experimental research design then such factors can have a great influence on the internal validity of the research.

f) Instrumentation:  It includes the way change in the dependent variable is measured during the study.

The two basic threats to  external validity are:

1. Testing: The participation of people in the pre-test affects the reaction of people towards the treatment.

2. Selection of participants: People who have been selected as participants in the study differ from the population.


From the above study it has been concluded that experimental research design generally has both internal and external validity. Another thing which has been concluded from the above is that Ensuring the internal validity of experimental research is very much important before applying any of the treatments. It has also been concluded that external validity is the core stone of an effective experimental design.

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