1.
Variables that may produce effects that can be mistaken for
effects of stimulus thereby invalidating internal validity
1.1.
History:
events taking place between the first and second measurements in addition to
the experimental variable
1.2.
Maturation: processes affecting the subjects of study (e.g., respondents)
operating as a function of the time
1.3.
Testing:
effects of taking a test on scores of the second test
1.4.
Instrumentation: effects on subjects of changes in calibration of a measuring
instrument or changes in the observers or scorers
1.5.
Statistical Regression: operating where groups have been selected on the
basis of their extreme scores
1.6.
Biases:
this can result to the differential selection of respondents for the comparison
groups
1.7.
Experimental mortality: loss of respondents from the comparison groups
1.8.
Selection-maturation interaction, etc.: comparison groups may react differently to
maturation and other variables and not to the treatment
2.
Variables that may produce effects mistaken for effects of
treatment thereby invalidating external validity
2.1. Reactive or
interaction effect of testing: pretest may increase or decrease the respondent’s sensitivity or
responsiveness to the experimental variable and thus make the results obtained
for a pretested population unrepresentative of the effects of the experimental
variable for the unpretested universe from which the experimental respondents
were selected
2.2. Interaction
effects of selection biases and the experimental variables:
2.3. Reactive effects
of experimental arrangements: the research or experimental situation itself can preclude
generalization because the situation to which the findings of a research or an
experiment are being generalized is a non-experimental setting
2.4. Multiple-treatment
interference:
whenever multiple treatments are applied to the same respondents, the effects
of prior treatments are not usually eraseable
Prof. Art Boquiren Dec 03
based on Campbell & Stanley 1966:5-6