Unformatted text preview: n Sample size:
n= ˆ
ˆ ∗/
p (1 − p )zα2 2
ME 2 ˆ
Most conservative sample size (if p is unknown)
n= ∗
(.5)(.5)zα2 2
/ h2 Sampling Distribution of the Sample Proportion (continued Checkpoint 3  Modeling and Inference
Sampling Distribution of the Sample Proportion Example
A poll of 120 adults found that 38% of the sample said
that they believe in the existence of life after death.
1. Find the margin or error for this poll if we want 95%
conﬁdence in our estimate of the percent of adults who believe
in life after death.
2. Explain what the ME means.
3. If we want a 99% conﬁdent, will the margin of error be
larger or smaller?
4. Find the ME needed to be 99% conﬁdent
5. Find the sample size needed to estimate the proportion of
believers within 3% with a conﬁdence level of 98%.
6. Suppose we want to cut the margin of error to 1%. What is
the necessary sample size? Sampling Distribution of the Sample Proportion (continued Checkpoint 3  Modeling and Inference
Sampling Distribution of the Sample Proportio...
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 Spring '08
 Ioudina
 Normal Distribution, Standard Deviation, Modeling and Inference

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