Learn Before
Explain why the researcher's argument is incorrect using the concepts of equivalent groups and systematic pre-existing differences.
Case context: A researcher is conducting a between-subjects study on the effects of a new study strategy on exam performance. Rather than using a random process, the researcher allows participants to sign up for either the morning session (which will use the new strategy) or the evening session (which will use the standard strategy). The researcher argues that because all participants are college students, the groups will be highly similar.
Question: Explain why the researcher's argument is incorrect using the concepts of equivalent groups and systematic pre-existing differences.
Sample answer: The researcher's argument is incorrect because they did not use random assignment to allocate participants, which is necessary to create equivalent groups. By letting participants choose their session time, the resulting groups are likely to have systematic pre-existing differences (such as work schedules, morning alertness, or chronotype), meaning the groups cannot be expected to be highly similar or equivalent.
Key points:
- Equivalent groups require random assignment to allocate participants.
- Allowing self-selection based on session time introduces systematic pre-existing differences.
- Without random assignment, groups cannot be assumed to be highly similar or equivalent.
Rubric: The response must explain that failing to use random assignment prevents the groups from being equivalent (2 points). It must identify that the self-selection method introduces systematic pre-existing differences (2 points) and explain that the groups are therefore not highly similar (1 point).
0
1
Tags
KPU
Research Methods in Psychology - 4th American Edition @ KPU
Related
When researchers use random assignment to allocate participants to different conditions, they expect the resulting groups to lack systematic pre-existing differences. What is the term used to describe these highly similar groups?
When researchers create 'equivalent groups' for an experiment, it means the groups are expected to be similar on average even though the individual participants within them are not identical.
A researcher is conducting a study comparing how different types of background noise affect reading comprehension. Order the steps the researcher should take to ensure they are starting the experiment with equivalent groups.
In psychological research, achieving control requires researchers to analyze the relationship between their assignment methods and the resulting characteristics of their conditions. Match each concept to the functional role it plays in establishing a valid comparison between groups.
In experimental research, what is the defining characteristic of 'equivalent groups'?
Arrange the logical stages involved in establishing 'equivalent groups' for a between-subjects experiment.
A researcher evaluates a between-subjects experiment and discovers that participants were assigned to conditions based on their level of prior experience with the task. The researcher must conclude that the study fails to utilize _____ groups because this method allowed for systematic pre-existing differences to influence the results.
A researcher randomly assigns 40 participants to either a treatment group or a control group in a between-subjects experiment. A skeptical colleague argues that the two groups cannot truly be 'equivalent' because every individual participant is unique and no two people are alike. This objection correctly challenges the logic of equivalent groups in between-subjects experimental design.
A researcher designing a between-subjects experiment must understand how key concepts relate to establishing—or undermining—equivalent groups. Match each term to the role it plays in that process.
A graduate student presents a between-subjects study in which participants who were already experiencing high stress were allowed to choose whether they joined the stress-reduction workshop group or the no-treatment control group. A faculty advisor evaluating the study concludes that any difference in post-study stress scores cannot be confidently attributed to the workshop alone, because the two groups are _____, meaning pre-existing participant differences—rather than the treatment itself—could explain the observed outcome.
Based on the concept of equivalent groups in a between-subjects experiment, define what makes groups equivalent and identify the specific procedure researchers must use to achieve this state.
Explain why the researcher's argument is incorrect using the concepts of equivalent groups and systematic pre-existing differences.
A cognitive psychologist wants to set up a between-subjects experiment to compare two types of memory training. How should they apply random assignment to ensure their experimental groups are equivalent?