Suppose that a researcher has conducted a simple experiment to assess the effect of background noise level on verbal learning. The manipulated independent level is the level of white noise in the room (group 1 = low level = 65 decibels (dB); group 2 = high level = 70 decibels). (Here are some approximate reference values for decibel noise levels: 45 dB, whispered conversation; 65 dB, normal conversation; 80 dB, vacuum cleaner; 90 dB, chain saw or jack hammer; 120 dB, rock music played very loud). The outcome measure is number of syllables correctly recalled from a 20-item list of nonsense syllables. Participants ranged in age from 17 to 70 and had widely varying levels of hearing acuity; some of them habitually study in quiet places and others prefer to study with the television or radio turned on. There were five participants in each of the two groups. The researcher found no significant difference in mean recall scores between these groups.
a. Describe THREE specific changes to the design of this noise/learning study that would be likely to increase the size of the t ratio (and therefore, make it more likely that the researcher would find a significant effect.)
b. Also: suppose that the researcher has reason to suspect that there is a curvilinear relation between noise level and task performance. What change would this require in the research design?