Hearing aids must be fit individually. A common way to test whether a particular hearing aid is right for a patient is to play a tape on which 25 words are pronounced clearly but at low volume, and ask the patient to repeat the words as heard. Different lists are available that are supposed to be of equal difficulty to understand correctly. However, a major problem for those wearing hearing aids is that the aids amplify background noise as well as the desired sounds. Are the test lists still equally difficult to understand in the presence of background noise?
In this experiment, 24 subjects with normal hearing listened to standard audiology tapes of English words at low volume, with a noisy background. They repeated the words and were scored correct or incorrect in their perception of the words. The order of list presentation was randomized.
A two-way ANOVA with "Hearing" as the dependent variable and "List" and "Subject" as factors assesses whether the different lists are equally difficult to understand while removing the effect of differences in hearing among the subjects. This design results in only one observation per cell since there are 96 observations, 24 subjects and 4 lists (24x4 = 96).