When using a nonequivalent group design what is the greatest threat to internal validity?
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Published on May 1, 2020 by Pritha Bhandari. Revised on October 10, 2022. geInternal validity is the extent to which you can be confident that a cause-and-effect relationship established in a study cannot be explained by other factors. In other words, can you reasonably
draw a causal link between your treatment and the response in an experiment? Internal validity makes the conclusions of a causal relationship credible and trustworthy. Without high
internal validity, an experiment cannot demonstrate a causal link between two variables. Once they arrive at the laboratory, the treatment group participants are given a cup of coffee to drink, while control group participants are given water. You also give both groups memory tests. After analyzing the results, you find that the treatment group performed better than the control group on the memory test. Can you conclude that drinking a cup of coffee improves memory performance? For your conclusion to be valid, you need to be able to rule out other explanations for the results. How to check whether your study has internal validityThere are three necessary conditions for internal validity. All three conditions must occur to experimentally establish causality between an independent variable A (your treatment variable) and dependent variable B (your response variable).
In the research example above, only two out of the three conditions have been met.
Because you assigned participants to groups based on the schedule, the groups were different at the start of the study. Any differences in memory performance may be due to a difference in the time of day. Therefore, you cannot say for certain whether the time of day or drinking a cup of coffee improved memory performance. That means your study has low internal validity, and you cannot deduce a causal relationship between drinking coffee and memory performance. Receive feedback on language, structure and formattingProfessional editors proofread and edit your paper by focusing on:
See an example Trade-off between internal and external validityExternal validity is the extent to which you can generalize the findings of a study to other measures, settings or groups. In other words, can you apply the findings of your study to a broader context? There is an inherent trade-off between internal and external validity; the more you control extraneous factors in your study, the less you can generalize your findings to a broader context. Research exampleIn your study of coffee and memory, the external validity depends on the selection of the memory test, the participant inclusion criteria, and the laboratory setting. For example, restricting your participants to college-aged people enhances internal validity at the expense of external validity – the findings of the study may only be generalizable to college-aged populations.Threats to internal validity and how to counter themThreats to internal validity are important to recognize and counter in a research design for a robust study. Different threats can apply to single-group and multi-group studies. Single-group studiesResearch example (single-group) A research team wants to study whether having indoor plants on office desks boosts the productivity of IT employees from a company. The researchers give each of the participating IT employees a plant to place by their desktop for the month-long study. All participants complete a timed productivity task before (pre-test) and after the study (post-test).
How to counter threats in single-group studiesAltering the experimental design can counter several threats to internal validity in single-group studies.
Multi-group studiesResearch example (multi-group)A researcher wants to compare whether a phone-based app or traditional flashcards are better for learning vocabulary for the SAT. They divide 11th graders from one school into three groups based on baseline (pre-test) scores on vocabulary. For 15 minutes a day, Group A uses the phone-based app, Group B uses flashcards, while Group C spends the time reading as a control. Three months later, post-test measures of vocabulary are taken.
How to counter threats in multi-group studiesAltering the experimental design can counter several threats to internal validity in multi-group studies.
Frequently asked questions about internal validitySources in this articleWe strongly encourage students to use sources in their work. You can cite our article (APA Style) or take a deep dive into the articles below. This Scribbr article
Is this article helpful?You have already voted. Thanks :-) Your vote is saved :-) Processing your vote... What is the major problem with the nonequivalent control group design?nonequivalent groups renders a design vulnerable to all internal validity threats because it is difficult to determine whether posttest differences are attributable to a treatment effect or preexisting group differences.
What is the disadvantage of non equivalent control group design?Conclusion: The non-equivalent control group post-test-only design can be used in natural settings, where randomisation cannot be conducted for ethical or practical reasons. Although the design is less complex than some other designs, with low error propagation, it is vulnerable to threats to internal validity.
Which design has the strongest internal validity?Of the three types of research, experimental, correlational and quasi-experimental, experimental research usually has the highest internal validity.
What is a nonequivalent group design?Nonequivalent Groups Design
When participants are not randomly assigned to conditions, however, the resulting groups are likely to be dissimilar in some ways. For this reason, researchers consider them to be nonequivalent.
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