Question 1: Using SPSS, calculate a 95% confidence interval for mean FEV1.
To do this we choose Analyze, Descriptive Statistics, Explore, variable FEV1, OK.
We get the following output:
Descriptives | ||||
---|---|---|---|---|
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.