II - Confounding and Obscuring Variables Flashcards
Maturation
A threat to internal validity that occurs when an observed change in an exp gp g erimental group could have emerged more or less spontaneously over time. E.g., Spontaneous remission
History threat
A threat to internal validity that
occurs when it is unclear whether a change in
the treatment group is caused by the
treatment or by a historical event that affects
everyone or almost everyone in the group.
The event must affect the group systematically, not
unsystematically
Regression threat
A threat to internal validity
related to regression toward the mean, by
which any extreme finding is likely to be closer
to its own typical, or mean, level the next time
it is measured (with or without the
experimental treatment or intervention).
An unusually good performance or outcome is likely
to regress downward; an unusually bad
performance or outcome is likely to regress upward.
When the people measured in a pretest
condition are extreme on the dependent
variable, regression is likely to be a threat to
internal validity.
If the comparison group and the experimental
group are equally extreme at pretest, the
researchers can account for any regression
effects in their results
Attrition
In a repeated-measures experiment
or quasi-experiment, a threat to internal
validity that occurs when a systematic type of
participant drops out of a study before it ends.
Sometimes called Sometimes called mortality “mortality”
Testing threat
: In a repeated-measures
experiment or quasi-experiment, a kind of
order effect in which scores change over time
just because participants have taken the test
more than once.
Instrumentation threat
A threat to internal
validity that occurs when a measuring
instrument changes over time from having
been used before.
Also called instrument decay Also called instrument decay.
Observer Bias
A bias that occurs when
observers’ expectations influence their
interpretation of the subjects interpretation of the subjects behaviors or the ’ behaviors or the
outcome of the study.
Can be a threat to internal validity in almost any
study in which there is a behavioral dependent
variable.
Observer bias can threaten internal and construct
validity in an experiment.
Demand characteristics
Cues that lead
participants to guess a study’s hypotheses or
goals.
Placebo effect:
An effect that occurs when
people receiving an experimental treatment
experience a change only because they
believe they are receiving a valid treatment.
Placebo group: A control group that is exposed to
an inert treatment (e.g., a sugar pill)
Double-blind placebo control study:
A study that
uses d l b a treatment group and a placebo group
and in which neither the research assistant nor
th i i k h i i hi h e participants know who is in which group
Null effect
A finding that an independent
variable did not make a difference in the
dependent variable - that there is no significant
covariance between the two.
Ceiling effect
An experimental design problem
in which independent variable groups score
almost the same on a dependent variable, such
that all scores fall at the high end of their
possible distribution.
Asking math questions too easy, everyone gets them right
Floor effect
An experimental design problem in
which independent variable groups score
al t th d d t i bl h lmost the same on a dependent variable, such
that all scores fall at the low end of their
possible distribution
asking math problems too hard, nobody gets them right
Reverse-Confound
confounds can apply to null effects too apply to null effects, too.
A study might be designed in such a way that a
conf d t ll t t t ff t found actually counteracts some true effect
of an independent variable.
