Chapter 8- Experimental Designs: Between-Subjects Design Flashcards
within-subjects design
a research design in which the different groups of scores are all obtained from the same group of participants. Also known as repeated-measures design.
BETWEEN-SUBJECTS DESIGN
A research design in which each of the different groups of scores is obtained from a separate group of participants. Also known as an independent-measures design.
between subjects experimental design (independent-measures experimental design)
an experimental design using a separate, independent group of individuals for each treatment condition being compared. Also known as an independent-measures experimental design.
individual differences
are personal characteristics that differ from one participant to another
Individual Differences as Confounding Variables:
Confounding From Individual Differences
Individual differences are any participant characteristics that can differ from one participant to another. If these characteristics are different from one group to another, then the experiment is confounded. For example, the participants in one group may be older, smarter, taller, or have higher socioeconomic status than the participants in another group. One group may have a higher proportion of males or a higher proportion of divorced individuals than another group. Any of these variables may produce differences between groups that can compromise the research results.
Individual Differences as Confounding Variables:
Confounding From Environmental Variables
Environmental variables are any characteristics of the environment that may differ. If these variables are different between groups, then the experiment is confounded by environmental variables. For example, one group may be tested in a large room and another group in a smaller room. Or one group may be measured primarily during the morning and another group during the afternoon. Any such variable may cause differences between groups that cannot be attributed to the independent variable.
equivalent groups
Created equally. The process used to obtain participants should be as similar as possible for all of the groups.
Treated equally. Except for the treatment conditions that are deliberately varied between groups, the groups of participants should receive exactly the same experiences.
Composed of equivalent individuals. The characteristics of the participants in any one group should be as similar as possible to the characteristics of the participants in every other group.
restricted random assignment
A random process for assigning individuals to groups that has a limitation to ensure predetermined characteristics (such as equal size) for the separate groups.
matching
The assignment of individuals to groups so that a specific variable is balanced or matched across the groups.
variance
A measure of variability obtained by computing the average squared distance from the mean.
variance within treatments (variance within groups)
A measure of the differences between scores for a group of individuals who have all received the same treatment. The intent is to measure naturally occurring differences that have not been caused by a treatment effect. Also known as variance within groups.
differential attrition
A threat to internal validity that occurs when attrition in one group is systematically different from the attrition in another group.
diffusion
A threat to internal validity that occurs when a treatment effect spreads from the treatment group to the control group, usually from participants talking to each other.
compensatory equalization
A threat to internal validity that occurs when an untreated group demands to receive a treatment that is the same as or equivalent to the treatment received by another group in the research study.
compensatory rivalry
A threat to internal validity that occurs when an untreated group learns about special treatment received by another group, then works extra hard to show they can perform just as well as that group.
