A psychologist is conducting an experiment to investigate the effects of a new brain-training application on focus. She plans to use an independent groups design where she personally trains the experimental group using the application and the control group using a standard word puzzle, and then assesses their focus levels herself.
Which of the following adjustments to her research design would be most effective in minimizing the impact of both investigator effects and demand characteristics?
Switching to a repeated measures design where all participants use both the brain-training application and the standard word puzzle.
Utilizing a double-blind procedure where an independent assistant, unaware of which group is which, administers the training and conducts the focus assessment.
Implementing a matched-pairs design based on the participants' initial academic performance.
Providing a comprehensive retrospective debrief to all participants immediately after their focus assessment is complete.
