Suggested answer to exercise: Confidence intervals for mean FEV1,3

Question 3: Calculate a 90% confidence interval for mean FEV1.

Suggested answer

To do this we choose Analyze, Descriptive Statistics, Explore, variable FEV1, as before. We then click Statistics and change the Confidence Interval for Mean from 99 to 90, Continue, OK.

We get the following output:

Statistic Std. Error
FEV1 (litre) Mean 4.0607 .08895
90% Confidence
Interval for Mean
Lower Bound 3.9119
Upper Bound 4.2095
5% Trimmed Mean 4.0561
Median 4.1000
Variance .451
Std. Deviation .67153
Minimum 2.85
Maximum 5.43
Range 2.58
Interquartile Range .99
Skewness .064 .316
Kurtosis -.857 .623

The 99% confidence interval is 3.9119 to 4.2095 litres.

To two decimal places, this is 3.91 to 4.21 litres.

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Last updated: 6 October, 2006.

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