PSYCHOLOGY CHAPTER 8

administration of a postest to a single group of participants after they have been given an experimental treatment condition

allows no evidence of what the participants would have scored on the DV had they not received the treatment

no control group

Design in which a treatment condition is interjected between a pretest and postest of the dependent variable (can compare pretest and postest)

In most cases --> are unaware if the sources of the rival hypotheses affect the results

Can be used to provide some info

design in which the performance of an experimental group is compared with that of a nonequivalent control group at the posttest

can test whether or not the independent variable influenced the dependent variable

selection poses a problem

does not exclude possible selection effects from the treatment effect

the participants in the comparison group might differ in important ways from the participants in the experimental group

threat to internal validity

the group of participants that does not receive the active treatment condition and serves as a standard for comparison for determining whether the treatment condition produced any causal effect

serves as a source of comparison

serves as a control for rival hypotheses

groups are produced by random assignment, and the different groups are exposed to different levels of the independent variable

posttest-only control-group design

pretest-posttest control-group design

administration of posttest to two or more randomly assigned groups of participants that receive the different levels of the independent variable

provides necessary equivalence on extraneous variables by randomly assigning participants to two or more groups (randomized control group)

threats to internal validity are controlled for

• weaknesses
• does not provide complete assurance that the necessary equivalence has been attained
• lacks a pretest and statistical power
• strengths
• combination of inclusion of a control group and random assignment produce a strong design for eliminating threats to internal validity

administration of a posttest to two or more randomly assigned groups of participants after the groups of participants have been pretested and administered the different levels of the independent variable

threatened only if one of the threats acts differently

advantages

• able to see how well the randomization process worked
• able to see if the relationship between the IV and the DV depends on other potentially important IVs
• ceiling effect
• gain empirical demonstration of whether the treatment condition succeeded in producing a change in research participants

disadvantages

• participants might change in some way because they were given a pretest

all participants receive all conditions

also called repeated measures designs

strengths

• participate in all experimental conditions
• does not require as many participants

weaknesses

• can be taxing on participants
• confounding influence of a sequence effect

strengths

• include many IVs in a study

weaknesses

• increase in the number of research participants required
• incorporating more than two IVs --> simultaneous manipulations
• higher-order interaction effects are significant