Quasi-experimental designs Flashcards
(15 cards)
what is a quasi experiment?
- involve manipulation of an IV or introduction of a treatment
- Often lack randomization/random assignment
- One-group posttest-only design
- One-group pretest-posttest design
Threats to internal validity controlled by true experiments
(and that often exist in quasi-experiments)
- History: Events that occur during participation that
affect behavior - Maturation: Changes due to the passage of time
that affect behavior - Testing: Taking a test can affect subsequent testing
- Instrument Decay: Changes in measurement
instruments (including observers) over time - Regression toward the mean: Extreme scores are
likely to be followed by more moderate scores - Subject attrition (mortality): Participants selectively
drop out of experiment. - Selection: When control and experimental groups
are chosen in such a way that they are not equivalen
what is a Nonequivalent control group design?
- Uses an experimental group and control group, but
they are not equivalent (e.g., natural groups) - Groups are “self-selecting”
example: Evaluate effects of regular writing exercises on writing quality; One lab does exercises, other lab does not
what is nonequivalent control group pretest-posttest design?
Nonequivalent groups (use pretest to show equivalence; or use pretest to show differential change for the two groups)
Possible additional problems: Different Section Leaders (a
confound), observer bias, contamination
what is One-group posttest-only design?
you have one group, give them a treatment, then measure them after.
(No “before” measurement.)
what is One-group pretest-posttest design?
You have one group, measure them before, give them a treatment, then measure them after.
what is an interrupted time-series design?
Examine a series of
observations before and after a treatment and look for a
change in behavior
EX) record attendance many days before and after
introducing quizzes
what is a Control series design (Multiple-group time-series design)?
interrupted time series design with a control group
what are Single case experimental designs?
- NOT case studies
- Traditionally used in studies of reinforcement and
behavior modification - Researcher manipulates an IV (unlike case study)
- Behavior recorded during baseline period – description
of behavior as it exists and as it would be in the future
without introduction of a treatment - Behavior is recorded after treatment is introduced
what are Reversal design (or ABA, or ABAB,…)?
A = baseline period (no treatment)
B = treatment period
You start without treatment (A), then give treatment (B), then take it away (A) — and sometimes bring it back (B) again.
what is a Multiple baseline design?
- Measure baseline in several situations (e.g.
aggressive behavior at home, school, and day care) - Introduce treatment at different times in the
different situations - Evidence for treatment effectiveness is that
behavior changes only when the treatment is
introduced
what is Multiple baseline across situations?
you apply the treatment in different settings one at a time.
(Example: Start helping a child speak more at home, then later at school, then later at daycare.)
what is Multiple baseline across subjects?
you apply the treatment to different people one at a time.
(Example: Teach child 1 to tie shoes, wait, then teach child 2, then child 3.)
what is Multiple baseline across behaviors?
You apply the treatment to different behaviors for the same person one at a time.
(Example: Help one child first with talking politely, then later with raising their hand, then later with doing homework.)
Problems that even true experiments may not control:
Contamination: Communication between
participants
Experimenter expectancy effects: The researcher’s expectations accidentally influence the participants’ behavior
Observer bias: The researcher sees what they want to see when measuring or judging behavior.
Novelty effects (Hawthorne effect): reactivity; when
participants behave differently because they know
they are being studied
