Suggested answer to exercise: Transformations, 1

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

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.

Back to Exercise: Transformations.

This page maintained by Martin Bland.
Last updated: 27 July, 2009.