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Exercise: Comparing means, 4

Question 4. What method would be used to calculate the confidence interval, and why?

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Suggested answer

What condition should the data meet for this method?
This is a comparison of two samples, so we would use an unpaired or two sample t method.
The data should be from Normal distributions with the same variance
for the standard two sample t method.
However, in this study the standard deviations in the two samples are very different,
48.7 µmol/L in study patients compared with 14.3 µmol/L in controls.
We should therefore use the two sample t method for unequal variances, the
Satterthwaite correction to the degrees of freedom.

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Last updated: 27 July, 2009.

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