History-- The different events which occurs
between the two consecutive measurements can affect the
validity.
Maturation-- The different processes in
different subjects which perform as a function of the time which
indicates that if a project continues for some years, the
performance of many participants will be improved.
Testing-- The outcomes of a test which has the
influence on the outcome of other tests.
Instrumentation-- Any kind of alteration in
the scorers, instrument, observers which can have some changes in
the final results can also impact validity.
Statistical regression-- It is also famous as
regression to the mean. This has mainly resulted from the subject
selection depending on the extreme scores.
Selection of subjects-- The validity can also
be threatened due to the biases in the selection of comparison
groups. This can be overcome by random selection.
Experimental mortality-- This is mainly the
result of the loss of subject. The different subjects who remain
with the team till the completion are motivated to learn a lot and
thus have greater performance level.
John Henry effect-- John Henry was mainly an
employee who outperformed a machine while conducting an experiment
as he knew that his performance is being measured against the
machine.