Three graphs, a scatter diagram, a histogram with superimposed Normal distribution curve, and a Normal plot.
The scatter diagram has the categorical variable Group on the horizontal axis with two categories: "Crohn's" and "Coeliac". The vertical axis is labeled "Log skinfold" and numbered 0, 0.5, 1, and 1.5.
There are two columns of points. The Crohn's column goes from log skinfold = 0.25 to log skinfold = 1.1 and the Coeliac column from log skinfold = 0.25 to log skinfold = 0.8. Points are closer together near the bottoms of the columns than near the tops, but less so than for the skinfolds themselves.
The histogram is for log skinfold minus mean, that is, the residuals within groups. The histogram looks quite symmetrical, though the small numbers makes it hard to be sure. The Normal distribution curve extends below the smallest residual and above the highest.
The Normal plot has log skinfold minus mean on the vertical axis and Inverse Normal on the horizontal axis. The line of points follows the straight line of perfect Normal distribution quite closely.
Back to Clinical Biostatistics: Transformations.
This page maintained by Martin Bland.
Last updated: 3 August, 2006.