A threat to internal validity occurs only if a potential design confound varies ________ with the independent variable.
Systematically
An independent-groups design is also known as a ________.
Between-subject design
Which of the following is a threat to internal validity found in within-groups designs but not in independent-groups designs?
Practice effects
Generally, what is the main priority for experimental studies?
Internal validity
Which of the following cannot be found in a one-group, pretest/posttest design?
A comparison group
To be a history threat, the external event must occur:
Systematically, affecting most members of the group
A decrease in participants' scores on a measure from pretest to posttest could suggest all of the following threats to internal validity EXCEPT?
Attrition
A researcher's attempt to control sounds, smells, and even temperature in a testing environment is meant to reduce which of the following?
Situation noise
Dr. Rhodes notices an interaction in his factorial study. In describing this, which statement might he use to explain the link between Independent Variable A and Independent Variable B in predicting the dependent variable?
The effect of Variable A depends on Variable B.
According to the textbook, why is it important to study interactions?
Many outcomes in psychology are interactions.
Imagine that you are reading a journal article and you see the following sentence: "The study used a 2 × 2 × 4 design." Based on this sentence alone, you would know all of the following pieces of information EXCEPT:
The number of participants in the study
Which of the following is a within-groups quasi-experimental design?
Interrupted time-series design
Which of the following is true of the difference between large-N and small-N experiments?
Each person in a small-N design is treated as a separate experiment
Which of the following is NOT a small-N design?
Interrupted time-series design
According to the textbook, which of the following ethical questions might be posed specifically in reference to a reversal design?
Is it ethical to remove an effective treatment?
Reasons researchers do experiments
*to have more valid study
*to make causal claims
*to generalize to more ppl
*to collect evidence in the real world
*to be the most scientific
Manipulated variables
researcher assigns participants to a particular level of the variable
Measured variables
researcher records what happens in terms of behavior or attitudes based on self-report, behavioral observations, or physiological measures
Control groups
no treatment
Treatment Group
treatment condition
Placebo group
placebo control
Confounds
a general term for a potential alternative explanation for a research finding (threat to internal validity)
Selection effect
a threat to internal validity that occurs in an independent-groups design when the kinds of participants at one level of the IV are systematically diff't from those at the other level
Independent-grps design
an experimental design in which different gaps of participants are exposed to diff't levels of the independent variable (etc. part. experiences only ONE level of the IV
W/in group designs
an experimental design in which ea. participant is presented with ALL levels of the IV
Order effects
when being exposed to one condition affects how participants respond to other conditions
Design confound (threat to Internal Validity)
a 2nd variable that unintentionally varies systematically with the independent variable
Selection Effect ( threat to internal validity)
in an independent-grp design, when the 2 independent grps have systematically diff't kinds of participants in them
Order effect (threat to internal validity)
in a with-in groups design, when the effect of the independent variable is confounded with carryover from one level to the other, or with practice, fatigue or boredom
Maturation (threat to internal validity)
an experimental gap improves over time only b/c of natural development spontaneous improvement
History (threat to internal validity)
an experimental group changes over time because of an external factor or event that affects all or most members of the group
Regression to the Mean (threat to internal validity)
an experimental group whose average is extremely low (or high) at pretest will get better (or worse) over time, because the random events that caused the extreme pretest scores do not recur the same way at posttest
Attrition (threat to internal validity)
An experimental group changes over time, but only because the most extreme cases have systematically dropped out and their scores are not included in the posttest
Testing (threat to internal validity)
A type of order effect: An experimental group changes over time because repeated testing has affected the participants. Subtypes include fatigue effects and practice effects
Instrumentation (threat to internal validity)
An experimental group changes over time, but only because repeated measurements have changed the quality of the measurement instrument.
Observer bias (threat to internal validity)
an experimental group's ratings differ from comparison group's but only because the researcher expects the groups' rating to differ
Demand characteristic (threat to internal validity)
participants guess what the study's purpose is and changed their behavior to the expected direction
Placebo effect (threat to internal validity)
participants in an experimental group improve only because they believe in the efficacy of the therapy or drug they receive
Threat to Internal Validity
Design Confound; Selection Effect; Order Effect; Maturation; History; Regression to the Mean; Attrition; Testing; Instrumentation; Observer Bias;Demand Characteristic; Placebo Effect
Null Effects
A finding that an independent variable did not make a difference in the dependent variable; there is no significant covariance between the two.
Weak Manipulations
treatment too weak to affect DV; rerun with stronger manipulation
Insensitive Measures
DV cannot detect difference from treatment
Celling Effects
when the participants' scores on the DV are clustered at the high end; everyone gets the question right
Flooring Effects
♣ when the participants' scores on the DV are clustered at the low end; no one gets the question right
Measurement Error
any factor that can inflate or deflate a person's true score on the DV
Individual differences
Measures more ppl; uses a matched design; uses a repeated measures design
Reducing the effects of Individual Differences
*Change design: use w/in gap instead of independent group
*Add more participants
Situation noise
external distractions of any kind that obscure between-groups difference and cause variability within-groups
Power
The likelihood that a study will yield a statistically significant result when the IV really has an effect
Quasi-Experiments
A study that is similar to an experiment except that the researchers do not have full experimental control
Time-Series Design
One-grp Pretest-Posttest Design; Nonequivalent control grp design; Interrupted time-series design; nonequivalent control group interrupted time-series design (multiple time-series design)
