Threats
extremely low or extremely high performance at Time 1 is likely to be less extreme at Time 2
Regression threat
Free points
you're welcome
How are maturation threats prevented?
Add a control group
participants know which group they’re in but observers don’t.
masked study
The independent variable did not affect the dependent variable, so there is no significant covariance between the IV and the DV.
Null effect
A change in behavior that emerges spontaneously over time.
Maturation threats
when people receive a treatment and improve, but only because they believe they are receiving a valid or effective treatment.
Placebo effect
How are history threats prevented?
Use a pretest/posttest design with a control group
neither the participants nor the experimenters working with the participants know who is in the treatment group and who is in the control group
double-blind study
(Error Variance) too much unsystematic variability within groups.
Noise
A reduction in participant numbers from pretest to posttest.
Attrition threat
Bias caused by researchers’ expectations influencing how they interpret the results.
Observer bias
How can attrition threats be prevented?
When participants drop out of a study, remove their scores from the pretest average.
a special comparison group is used that is receiving the placebo therapy or placebo medication, but neither the people working with the participants nor the participants know who is in which group
Double-blind placebo control study
The participants’ scores on the DV are clustered at the high end
Ceiling effect
when some external or “historical” event affects most members of the treatment group at the same time as the treatment.
History threat
Occurs when a measuring instrument changes over time.
Instrumentation threat (aka instrumentation decay)
How can instrumentation threats be prevented?
–Use a posttest-only design
–counterbalance the order of the pretest and posttest forms
one group of participants is measured on a pretest, exposed to a treatment, intervention, or change, and then measured on a posttest.
One-group pretest/posttest design
The participants’ scores on the DV are clustered at the low end.
Floor effect
A type of order effect in which there is a change in participants as a result of experiencing the DV (the test) more than once.
Testing threat
What is the key difference between Instrumentation threats versus Testing threats
Instrumentation threats are when the instruments change over time. Testing threats are when participants change over time.
How can testing threats be prevented?
Use a Posttest design (no pretest)
Use alternative forms of the test at pretest and posttest
second DV included in a study to make sure the IV manipulation worked.
Manipulation check
Any factor that can inflate or deflate a person’s true score on the DV.
Measurement error