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 stress-free 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
Relatively stress free 26 31 25 26 30

Required:
1. The obtained value of the appropriate statistic is ___

a. tobt = -4.73
b. tobt = -4.71
c. tobt = -3.05
d. tobt = -.047

2. The df for determining tcrit are .

a. 4
b. 9
c. 8
d. 3

3. Using a = 0.052 tail, tcrit = .

a. +- 2.162
b. +- 2.506
c. +- 2.462
d. +- 2.306

4. Using a = .052 tail, your conclusion is .

a. Accept H0; stress does not affect the menstrual cycle
b. Retain H0; we cannot conclude that stress affects the menstrual cycle
c. Retain H0; Stress affects the menstrual cycle
d. Reject H0; stress affects the menstrual cycle

The degrees of freedom is number of independent variable factors that affect the range of parameters. The degrees of freedom is the calculation of number values that are free to vary. The degrees of freedom is calculated by N-1. Standard error is the estimated deviation of standard deviation from its sample mean distribution. The null hypothesis is rejected or accepted on the basis of level of significance. When the p-value is greater than level of significance we fail to reject the null hypothesis and null hypothesis is then accepted.