The following Exercise is based on summary statistics rather than raw data. This information is typically all that is presented in published reports. You can calculate inference procedures by hand from the summaries. Use the conservative Option 2 (degrees of freedom the smaller ofn

1

1

n

1

1

andn

2

1

n

2

1

for two-sample t confidence intervals and P-values. You must trust that the authors understood the conditions for inference and verified that they apply. This isn't always true.)

Equip male and female students with a small device that secretly records sound for a random 30 seconds during each 12.5-minute period over two days. Count the words each subject speaks during each recording period, and from this, estimate how many words per day each subject speaks. The published report includes a table summarizing six such studies. Here are two of the six:

Sample SizeEstimated Average Number

(SD) of Words Spoken per Day

StudyWomenMenWomenMen1 67 67 15096 (7459)16324 (9269)2 30 24 16008 (7577)12998 (8306)

Readers are expected to understand this to mean, for example, the 67 women in the first study hadx

x

= 15096 and s = 7459.

It is commonly thought that women talk more than men. Does either of the two samples support this idea? For each study:

(a) State the alternative hypothesis in terms of the population mean number of words spoken per day for men(

M)

(M)

and for women(F)(F)

. If necessary, use != to represent

.

Study 1:

M

M

F

F

Study 2:

M

M

F

F

(b) Find the two-sample t statistic to test

F

M

F

M

.

Study 1:

Study 2:

(c) What degrees of freedom does Option 2 use to get a conservative P-value?

Study 1:

Study 2:

(d) Compare your value of t with the critical values in Table C. What can you say about theP-value of the test?

Study 1:P-value>

>

Study 2:

P-value