1. 3 stat problems

1. x1 = 14, n1 = 20, x2 = 8, n2 = 20; right-tailed test, alpha = 0.05; 90% confidence interval

2. Of 21,300 men who had not had a vasectomy, 69 were found to have prostate cancer, of 22,000 men who had a vasectomy, 113 were found to have prostate cancer.
a. At the 1% sig level, do the data provide sufficient evidence to conclude that men who have had a vasectomy are at greater risk of having prostate cancer?
b. Is this study a designed experiment or an observational study? Explain your answer.
c. In view of your answers to part a and b, could you reasonably conclude that having a vasectomy causes an increased risk of prostate cancer? Explain your answer.

3. Independent random samples of white and african-american elderly (aged 70 or older). Of the 4989 white elderly surveyed, 529 had at least once stroke, whereas 103 of the 906 african-american elderly surveyed reported at least one stroke. At the 5% sig level do the data suggest that there is a difference in stroke incidence between white and african-american elderly? Find and interpret a 95% con interval for the dif between white and african-american elderly.

2. Those are nice problems. Perhaps you could demonstrate SOME understanding of the solutions.

Can you define a Null Hypothesis?
Can you differentiate between 1-tail and 2-tail tests?
Do you know when to use a t-statistic vs. a z-statistic?
What is the role of a "Critical Value"?
What is a "Rejection Region" and how does it work?

Help us out, here. I'm guessing you already have a textbook and a teacher. Will it REALLY help if we repeat what you know already? For this reason, please demonstrate what you know already.