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