Yue Bing is a new intern at LinkedIn. She has designed a new recommendation algorithm for connecting LinkedIn users to other users, and wants to see if it will cause an increase the average number of messages sent by LinkedIn users. She will randomly sample one group of users from the LinkedIn network and set up their accounts so that they use the new recommendation algorithm. She will then randomly sample another group of users, who will operate on the regular recommendation algorithm. She determines how many messages are sent by users over the course of year. She ends up assigning 22 users to the new algorithm, and 39 users to the old algorithm. She provides you with some of her data, though it is incomplete. Sample Size Sample Mean Standard Deviation
New 22 40.2 ??
Old 39 33.1 3.1
She insists all assumptions necessary for a confidence interval for a difference between two appropriate means have been verified. What distribution would we use to determine the critical value of a 95% confidence interval using her sample data?
Select one:
a. A Z distribution.
b. A T distribution with 22 degrees of freedom.
c. A T distribution with 60 degrees of freedom.
d. A T distribution with 38 degrees of freedom.
e. A T distribution with 39 degrees of freedom.
f. A T distribution with 21 degrees of freedom.