# Graph description: Comparing within-subject variances in a study to compare two methods of measurement, 2

This is what happens to the previous graph if log transgform the squared differences.

This is a scatter graph of the difference between the squared differences between the mini meter and the Wright meter after log transformation of the squared differences, mini minus Wright, against the mean of log transformed squared differences for the min meter and the Wright meter. Thus the vertical axis represents the variable found by calculating the difference between the two mini meter readings then squaring it and taking the logarithm, and subtracting the logarithm of the square of the difference between the two Wright meter readings. The horizontal axis shows the average of the mini meter difference squared and log transformed and the Wirght meter difference squared and log transformed. There is little evidence for non-Normal data. There is little to suggest a relationship between difference and mean and the log squared differences appear to have a reasonable distribution.

The graph also shows a horizontal line through zero. The differences (between the log squared differences for the two meters) tend to lie above this line, but not greatly so.

This page maintained by Martin Bland.
Last updated: 12 January, 2004.