Final answer:
The most correct statement about experimental research is that using a within-participants design can result in improved performance due to practice effects. Correlation coefficients indicate relationships but not causation, and experimental procedures should minimize bias.
Step-by-step explanation:
The statement about experimental research that is most correct is: Using a within-participants design may lead participants to get better at the task the second time they perform it. This effect is known as practice effect or carryover effect, and it is a common issue in within-participants or repeated measures designs where the same participants are exposed to all conditions of the experiment. Hence, to control for these practice effects, counterbalancing and other techniques are used. While a high correlation coefficient such as 0.9 does imply a strong relationship between two variables, it does not prove causation. Additionally, the procedural aspects of data collection and participant assignment should be structured to minimize bias and uphold the experimental integrity. Random assignment is usually utilized to help ensure that groups are equivalent at the start of the experiment.