Final answer:
Multiple-treatment interference is a threat to external validity in research studies, where the effects of one treatment can be influenced or confounded by the presence of other treatments. Researchers need to carefully design their studies to minimize this interference and ensure the accurate analysis of the specific treatment's effect.
Step-by-step explanation:
Multiple-treatment interference is a threat to external validity in research studies. It refers to the situation where the effects of one treatment can be influenced or confounded by the presence of other treatments. This can make it difficult to determine the true effect of a specific treatment on the outcome or response variable being measured.
For example, in a study comparing the effectiveness of different study methods on test scores, if all subjects experience multiple study methods instead of just one, the results may be influenced by the interactions and interference between the different methods, rather than solely reflecting the effect of a single method. This can compromise the validity and reliability of the study findings.
To minimize multiple-treatment interference, researchers need to carefully design their studies, considering the order in which treatments are administered, controlling for interactions between treatments, and ensuring that the effects of the specific treatment of interest can be isolated and analyzed accurately.