"Adults Who Stutter: Responses to Cognitive Stress," published in the Journal of Speech and Hearing Research in 1994, reported that speech rate, in words per minute, for 9 stutterers under conditions of stress had mean 52.6 and standard deviation 3.2.
a. Use the fact that the t multiplier for 8 degrees of freedom at 99% confidence is 3.36 to construct a 99% confidence interval for mean speech rate of all stutterers under conditions of stress.
b. If a lower level of confidence were desired, would the interval be wider or narrower?
c. If standard deviation had been larger than 3.2, would the interval be wider or narrower?
d. If the sample size had been smaller than 9, would the interval be wider or narrower?
e. If 3.2 were known population standard deviation, instead of sample standard deviation, would the interval be wider or narrower?