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 "Reciprocal skinfold" and numbered 0, 0.1, 0.2, 0.3, 0.4, 0.5, and 0.6.
There are two columns of points. The Crohn's column goes from Reciprocal skinfold = 0.1 to Reciprocal skinfold = 0.55 and the Coeliac column from Reciprocal skinfold = 1.4 to Reciprocal skinfold = 0.56. Points in the Crohn's colum appear fairly evenly spread, those in the Coeliac column appear to form two gorups with a gap in the middle.
The histogram is for Reciprocal 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 intervals and frequencies are: -3 to -2, 1; -2 to -1, 7; -1 to 0, 9; 0 to 1, 4; 1 to 2, 7; 2 to 3, 1.
The Normal distribution curve extends below the smallest residual and above the highest.
The Normal plot has 1/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, though not so well as does the log skinfold.
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This page maintained by Martin Bland.
Last updated: 3 August, 2006.