Internal validity refers to establishing a causal relationship between a treatment and outcome. Some threats to internal validity include history effects from outside events between pre- and post-testing, maturation effects from natural physical/intellectual changes, and testing effects from taking a pre-test influencing later tests. Other threats are instrumentation changes affecting measurements, regression toward the mean for extreme pre-test scores, mortality from participant dropout, diffusion of treatment between groups, and experimenter bias from expected outcomes influencing results.

1. Shayan Iqbal
Threats to internal
validity

2. Collaborative teaching
Students
Achievements in
mathematics

3. Internal validity is the extent
to which a study establishes a
trustworthy cause-and-effect
relationship between a
treatment and an outcome
Internal validity

4. History Specific events, in addition to the
treatment, that occur between the first
and second measurement.The longer the
interval between the pretest and
posttest, the more viable this threat
Historical event

5. Maturation Changes in physical,
intellectual, or emotional characteristics,
that occur naturally over time, that
influence the results of a research study.
In longitudinal studies, for instance,
individuals grow older, become more
sophisticated, maybe more set in there
ways.
Maturation

6. Testing Also called “pretest sensitization,” this
refers to the effects of taking a test upon
performance on a second testing. Merely
having been exposed to the pretest may
influence performance on a posttest.Testing
becomes a more viable threat to internal
validity as the time between pretest and
posttest is shortened.
Testing

7. Instrumentation Changes in the way a
test or other measuring instrument is
calibrated that could account for
results of a research study (different
forms of a test can have different
levels of difficulty).This threat
typically arises from unreliability in the
measuring instrument. Can also be
present when using observers
Instrumentation

8. Occurs when individuals are selected for
an intervention or treatment on the basis
of extreme scores on a pretest. Extreme
scores are more likely to reflect larger
(positive or negative) errors in
measurement (chance factors). Such
extreme measurement errors are NOT
likely to occur on a second testing.
Statistical Regression

9. Experimental mortality is only likely to
be a significant threat to internal validity
if the experiment lasts a long time, since
the potential for reasons for dropouts to
occur increase (e.g., geographical move,
apathy, problems of availability, etc.).
This is especially likely to be the case if
the treatment condition is particularly
demanding
Mortality

10. Sometimes the treatment and control
group participants are able to
communicate with each other.The
danger is that some aspects of the
experimental stimulus (i.e., the
intervention) are passed on from the
treatment group to the control group
(e.g., methods, materials, perspectives,
etc.); that is, there is an exchange of
information between the groups, which
influences the behaviour of the control
group.
Diffusion

11. Expectations of an outcome by
persons running an experiment may
significantly influence that outcome.
Experimenter bias

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