How confident? The figure at top right shows the result of taking SRSs from a Normal population and constructing a confidence interval for each sample. Which confidence level—, or —do you think was used? Explain.
The nearest confidence level is .
The result of taking SRSs:
The red lines under the curve represent the sample means that do not contain the true population proportion.
We note that there are out of the samples that do not contain the true proportion and thus out of the samples contain the true proportion:
The nearest confidence level is (although could also be a possible used confidence level).
In a poll,
I. Some people refused to answer questions.
II. People without telephones could not be in the sample.
III. Some people never answered the phone in several calls.
Which of these sources is included in the margin of error announced for the poll?
(a) I only
(b) II only
(c) III only
(d) I, II, and III
(e) None of these
Losing weight A Gallup Poll in November found that of the people in its sample said “Yes” when asked, “Would you like to lose weight?” Gallup announced: “For results based on the total sample of national adults, one can say with 95% confidence that the margin of (sampling) error is percentage points.”
(a) Explain what the margin of error means in this setting.
(b) State and interpret the confidence interval.
(c) Interpret the confidence level.
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