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Suggested answer to exercise: Transformations, 1

Question 1: Why was the logarithmic transformation of the data used?

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Suggested answer

From the figure we can see that the albumin data have skew distributions,
with a few observations much greater than the rest.
The variability is also much greater in the COAD patients where the mean is higher.
Using a logarithmic scale (see figure below) stretches the bottom of the scale
and compresses the top, making the distribution more like the Normal.

D

The log transformation also makes the variances more uniform.
The transformed data matches the assumptions of the t test more closely.

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Exercise: Transformations.

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Last updated: 27 July, 2009.