Chapter 8
between subject experimental design
(independent measures experimental design)
requires a separate, independent group of individuals for each treatment condition
individual differences
are personal characteristics that can differ from one participant to another
assignment bias
when characteristics in one group are significantly different from the participants in the other group
- created equally
- treated equally
- composed of equivalent individuals
when researcher has control over the assignment of individuals to groups, the groups must be
random assignment
a random process is used to assign participants to a group
restricted random assignment
the group assignment process is limited to ensure predetermined characteristics for the separate groups
matching
involves assigning individuals to groups so that a specific variable is balanced, or matched, across the groups
variance within treatments/groups
a measure of differences between scores for a group individuals who have all received the same treatment.
- standardizing procedures and treatment setting
- limit individual differences
- random assignment and matching
- sample size
how to minimize variance within treatments
differential attrition
differences in attrition rates from one group to another and can threaten the internal validity of a between-subjects experiment
diffusion
the spread of treatment from the experimental group to the control group, which tends to reduce the difference between the two conditions
compensatory equalization
an untreated group learns about the treatment being received by the other group, and demands the same or equal treatment
compensatory rivalry
the untreated group works extra hard to show that they can perform just as well as the individuals receiving the special treatment
resentful demoralization
participants in an untreated group simply give up when they learn that the other group is receiving special treatment.
two-group design
comparing only two groups of participants: the researcher manipulates one independent variable with only two levels
single-factor multiple-group design
research design comparing more than two groups of participants representing more than two levels of the same factor