# Chapter 1. Accurate Confidence Intervals for a Proportion

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Stat Tutor
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1:44

### Question 1.1

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Incorrect. We use a plus four confidence interval whenever the sample size is not large enough to use a large sample confidence interval.
Correct. We use a plus four confidence interval whenever the sample size is not large enough to use a large sample confidence interval.
Incorrect. Try again.
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2:34

### Question 1.2

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Incorrect. Sample size greater than 10 is large enough whenever the data are collected with an SRS. Note that sample size large does not depend on the value of p.
Correct. Sample size greater than 10 is large enough whenever the data are collected with an SRS. Note that sample size large does not depend on the value of p.
Incorrect. Try again.
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3:45

### Question 1.3

Incorrect. The researchers want to estimate the proportion of all patients with warts who could get rid of them using duct tape.
Correct. The researchers want to estimate the proportion of all patients with warts who could get rid of them using duct tape.
Incorrect. Try again.
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4:24

### Question 1.4

Incorrect. $$\widetilde{p}$$ = $$\frac{count \, of \, success \,+ \, 2}{n+4}$$ = $$\frac{22+2}{26+4}$$ = $$\frac{24}{30}$$ = 0.80
Correct. $$\widetilde{p}$$ = $$\frac{count \, of \, success \, + \,2}{n+4}$$ = $$\frac{22+2}{26+4}$$ = $$\frac{24}{30}$$ = 0.80
Incorrect. Try again.
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5:50

### Question 1.5

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Incorrect. The entire interval (0.66, 0.94) is greater than 0.5, so yes, over half of all patients who might use duct tape to get rid of their warts will be successful.
Correct. The entire interval (0.66, 0.94) is greater than 0.5, so yes, over half of all patients who might use duct tape to get rid of their warts will be successful.
Incorrect. Try again.
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