An international psychology researcher is invited by an elementary school in Bogota to conduct a study to investigate the impact of noise from a construction site proposed for a site close to the school on teachers' ability to effectively present class material.
The manipulated independent variable is identified as the likely levels of noise produced by the construction site (60 vs. 65 dB).
In a lab setting, ten teachers from the school are randomly assigned to each level of noise; these participants vary widely in age, hearing acuity, and teaching style.
The dependent variable is performance on a verbal learning task (how many words on a list of 25 words each participant remembers). The t value obtained is not statistically significant.
What advice would you give to the international psychologist about ways to redesign this study that might improve the chances of detecting an effect of noise on the verbal learning task?