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10.1 Estimating with Confidence
Statistical Inference
allows ways to conclude about a population from
a sample data.
Confidence Interval (CI)
is the interval that will contain the true
population parameter.
Calculation for a Confidence Interval
CI=estimate +
margin of error (MOE)
MOE
=
z
*
s
n
C=central area of graph
z*=invNorm[(C1)/2]
Step 1:
Population of interest in context with the question
Parameter of interest is population mean
Step 2:
State you are going to construct a C confidence interval and why
Don't forget the “because” and the
α.
Conditions:
The sample size is an SRS from the correct population
The distribution of xbar is normal
If any assumptions, caution it.
Assume
N m
,
d
(
)
=
N m
,
s
n
ae
è
ç
ö
ø
÷
Step 3:
Carry out the test.
CI=estimate +
margin of error (MOE)
Step 4:
Interpret the Confidence Interval
“I am C% confident that the (interval) contain the population mean”
and
“A C% confidence interval means that C% of intervals constructed by this method will
contain the population mean.
Restate any cautions made in step 2.
You can use the formula
MOE
=
z
*
s
n
to determine n if given the MOE.
As the MOE gets smaller
the confidence level C decreases
the population standard deviation decreases
the sample size n increases
10.2 Test of significance
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 Spring '09
 yesman

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