Final answer:
The use of random assignment in a study is key in providing evidence against confounding and differences between groups. Blinding and the presence of a control group further strengthen the study's validity by isolating the treatment effects from other variables.
Step-by-step explanation:
The question pertains to whether a particular study provides evidence against confounding and pre-existing differences between groups, which could impact the validity of the study's findings. When a study uses random assignment of participants to treatment groups, it is likely that lurking variables are evenly distributed between groups. The only intended difference between groups should be the treatment imposed by the researchers. Hence, any difference in outcomes is attributed to the treatment itself, supporting a cause-and-effect relationship between the explanatory and response variables.
To address potential confounding, researchers could implement blinding in the study, which means that participants and, in some cases, researchers do not know which treatment each participant receives. This method reduces the risk of bias in the results. Additionally, the inclusion of a control group, which receives a placebo or no treatment, helps to ensure that any change in the response variable can be attributed to the active treatment. If both the experimental and control groups are treated identically except for the active treatment, researchers can be more confident that differences in outcomes are due to the treatment rather than extraneous variables or confounding factors.