Altman's nomogram is a graph with two vertical scales and two sloping lines in the middle. On the left is a vertical scale for Standardizd difference. This is marked in equal intervals from 0.0 at the top to 1.2 at the bottom. On the right is a vertical scale for Power. This is marked in intervals of increasing size from from 0.995 at the top to 0.05 at the bottom. The upper sloping line is labeled significance level 0.05 and runs downwards to the right from 0.0 on the left axis at an angle of about 40 degrees to the axis to a level about 0.9 on the standardised difference scale. The lower sloping line is labeled significance level 0.01 and runs downwards to the right from 0.0 on the left axis at an angle of about 35 degrees to the axis to a level about 1.04 on the standardised difference scale. A scale is marked on the upper sloping line starting level with standardized difference = about 0.09 and reading 10000, 8000, 4000, 3000, 2000, 1400, 1000, 800, 600, 500, 400, 300, 240, 200, 160, 140, 120, 100, 80, 70, 60, 50, 40, 30, 24, 20, 16, 14, 12, 10, and 8. Other scale divisions are marked but not labeled. This scale is labeled N. Vertical lines link the scale on the upper sloping line to the lower sloping line. The sloping lines do not meet the left vertical axis.
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This page maintained by Martin Bland.
Last updated: 15 July, 2009.