Difference
between internal and external validity
Internal
and external validity are concepts that reflect whether or not the results of a
study are trustworthy and meaningful.
While internal validity relates to how well a
study is conducted (its structure), external validity relates to how applicable
the findings are to the real world( (‘Difference
Between Internal and External Validity (with Comparison Chart)—Key
Differences’, n.d.).
Figure
1.internal and external validity
Internal Validity
Internal validity is the extent to which
a study establishes a trust worthy cause and effect relationship between a
treatment and an outcome. It also reflects that a given study make it possible
to eliminate alternative explanations for a finding. For example, If you implement a smoking
cessation programme
with a group of individuals, how sure can you be that any improvement seen in
the treatment group is due to the treatment that you administered. In short,
you can only be confident that your study is internally valid if you can rule
out alternative explanation for your findings. As a brief summary, you can only assume cause
and effect when you meet the following three criteria in your study.
The cause preceded the effect in terms
of time.
The cause and effect vary together.
There are no other likely explanations
for this relationship that you have observed.
It depends largely on the procedures of
a study and how rigorously it performed.
It is not a yes or no type of concept
(instead, we consider how confident we can be with the findings of a study,
based on whether it avoids traps that may make the findings questionable.)
Factors that improve internal validity
includes Randomization, Random selection, Blinding, experimental manipulation, study
protocol.
Factors that threaten internal validity
confounding, historical events, maturation, testing, instrumentation, attrition,
diffusion, experimenter bias
External Validity
External validity refers to how well the
outcome of a study can be expected to apply to other settings. In other words,
this type of validity refers to how generalizable
the findings are. For instance, do the
findings apply to other people, settings, situations and time periods.
Ecological validity, an aspect of external validity, refers to whether a
study's findings can be generalized to the real world. Another term called
transferability relates to external validity and refers to the qualitative
research design. Transferability refers to whether results transfer to
situations with similar characteristics( (Gans
& MD, n.d.).
Factors that improve external validity involve inclusion and exclusion
criteria, Psychological realism, Replication, Field experiments, Reprocessing
or Calibration. Factors that threaten external validity includes situational
factors such as time of day, location, noise, researcher characteristics, pre-
and post test effect, sample features, selection bias etc.
The essential
difference between internal and external validity is that internal validity
refers to the structure of a study and its variables while external validity
relates to how universal the results are. There are further differences between the two
as well.
Table 1difference of internal and external validity
Table 1difference of internal and external validity
Basis for comparison
|
Internal validity
|
External
validity
|
Meaning
|
Internal validity is the extent to
which the experiment is free from errors and any difference in measurement is
due to independent variable and nothing else.
|
External validity is
the extent to which the research results can be inferred to world at large.
|
Concerned with
|
Control
|
Naturalness
|
What is it ?
|
It is a measure of accuracy of the
experiment
|
It
checks whether the casual relationship discovered in the experiment can be
generalized or not.
|
Identifies
|
How strong the research methods are?
|
Can
the outcome of the research be applied to the real world
|
Describes
|
Degree to which the conclusion is
warranted
|
Degree
to which the study is warranted to generalize the result to other context
|
Used to
|
Address or eliminate alternative
explanation for the result
|
Generalize the
outcome
|
Reference
https://key differences.com
Difference
Between Internal and External Validity (with Comparison Chart)—Key Differences.
(n.d.). Retrieved 20 August 2019, from
https://keydifferences.com/difference-between-internal-and-external-validity.html
Gans, S., & MD. (n.d.). Understanding Internal and
External Validity. Retrieved 20 August 2019, from Verywell Mind website:
https://www.verywellmind.com/internal-and-external-validity-4584479
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