Case Study 141
A professor of women's studies is interested in determining if stress affects the menstrual cycle. Ten women are randomly sampled for an experiment and randomly divided into two groups. One of the groups is subjected to high stress for two months while the other lives in a relatively stressfree environment. The professor measures the menstrual cycle (in days) of each woman during the second month. The following data are obtained.
High stress 
20 
23 
18 
19 
22 n11 
Relatively stress free 
26 
31 
25 
26 
30 n21 
__ 8. Refer to Case Study 141. The obtained value of the appropriate statistic is _________.
a. 
t_{obt} = 4.73 
b. 
t_{obt} = 4.71 
c. 
t_{obt} = 3.05 
d. 
t_{obt} = 0.47





____ 9. Refer to Case Study 141. The df for determining t_{crit} are _________.
a. 
4 
b. 
9 
c. 
8 
d. 
3 
____ 10. Refer to Case Study 141. Using a = .05_{2 tail}, t_{crit} = _________.
a. 
+2.262 
b. 
+2.306 
c. 
±2.262 
d. 
±2.306 
____ 11. Refer to Case Study 141. Using a = .05_{2 tail}, your conclusion is _________.
a. 
accept H_{0}; stress does not affect the menstrual cycle 
b. 
retain H_{0}; we cannot conclude that stress affects the menstrual cycle 
c. 
retain H_{0}; stress affects the menstrual cycle 
d. 
reject H_{0}; stress affects the menstrual cycle 
Case Study 142
A health educator wants to evaluate the effect of a dental film on the frequency with which children brush their teeth. A random selection of 8 children are used for the experiment. First, a baseline of the number of times the children brush their teeth over a month's period is established. Next, the children are shown the dental film and again the number of teeth brushings are recorded for a month. The following data are recorded.
Subject 
1 
2 
3 
4 
5 
6 
7 
8 
After film 
28 
29 
25 
30 
25 
27 
28 
24 
Baseline 
25 
28 
22 
30 
26 
24 
25 
22 
____ 14. Refer to Case Study 142. The obtained value of the appropriate statistic is _________.
a. 
3.13 
b. 
3.14 
c. 
3.58 
d. 
3.57

____ 15. Refer to Case Study 142. The df for determining t_{crit} equal _________.
a. 
8 
b. 
16 
c. 
7 
d. 
14 
____ 16. Refer to Case Study 142. Using a = .05_{2 tail}, t_{crit} = _________.
a. 
+2.365 
b. 
±2.365 
c. 
±2.145 
d. 
+2.365 
____ 17. Refer to Case Study 142. Using a = 0.05_{2 tail}, what do you conclude?
a. 
retain H_{0}; the film has no effect on the frequency of tooth brushing 
b. 
reject H_{0}; the film affects the frequency of tooth brushing 
c. 
accept H_{0}; the film has no effect on the frequency of tooth brushing 
d. 
reject H_{0}; chance alone is a reasonable explanation of the data 
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