Suggested answer to exercise: Confidence intervals for mean FEV1, 1

Question 1: Using SPSS, calculate a 95% confidence interval for mean FEV1.

Suggested answer

To do this we choose Analyze, Descriptive Statistics, Explore, variable FEV1, OK.

We get the following output:

Statistic Std. Error
FEV1 (litre) Mean 4.0607 .08895
95% Confidence
Interval for Mean
Lower Bound 3.8825
Upper Bound 4.2389
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

SPSS also gives other output, a stem and leaf plot and a box and whisker plot.

The 95% confidence interval is 3.8825 to 4.2389 litres.

To two decimal places, this is 3.88 to 4.24 litres.

As we know the units, litres, we should state them.

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Last updated: 31 January, 2012.

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