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:

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.

Back to Exercise: Confidence intervals for mean FEV1.

To Applied Biostatistics index.

To Martin Bland's M.Sc. index.

To Martin Bland's home page.

This page maintained by Martin Bland.
Last updated: 6 October, 2006.

Back to top.