Confidence Intervals for mu (when sigma is unknown)
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When sigma is unknown but n is larger than 40, you want to conduct a CI
that uses z.
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To do this, enter your data into C1. Then go to Stat, Basic Statistics,
1 sample z.
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Your screen should look like this.
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Enter the variable that you want and enter the sample standard deviation
as s. Now click on Options.
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Make sure that you entered the correct confidence level.
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Next pick the type of confidence interval or bound.
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If you want a confidence interval select, "not equal" as your alternative.
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If you want a confidence bound, select "less than" for a upper bound or
"greater than" for an lower bound.
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Your output may look like the following.
Note: Your screen may look a little different; however,
you should have the same boxes to fill in for Confidence and Alternative.
One-Sample Z: C2
The assumed sigma = 0.3
Variable N
Mean StDev SE Mean
95.0% CI
C2
40 5.6258 7.3789
0.0474 ( 5.5328, 5.7188)