Is Reduction of Pocket Probing Depth Correlated with the Baseline Value or is it "Mathematical Coupling"?
Y.-K. Tu1,
M.S. Gilthorpe1,*, and
G.S. Griffiths2
1 Biostatistics Unit, Academic Unit of Epidemiology and Health Services Research, Medical School, University of Leeds, 24 Hyde Terrace, Leeds, LS2 9LN, UK; and
2 Department of Periodontology, Eastman Dental Institute, University College London, 256 Gray’s Inn Road, London, WC1X 8LD, UK;
View larger version (13K):
[in a new window]
|
Figure 1. An illustration of mathematical coupling (MC) without any effect of regression to the mean (RTM). (A) True Y values plotted against true X values, with no underlying relationship between them. (B) A spurious correlation between true Z (= X - Y) and true X is shown; the solid line is the regression of Z on X; this represents the hypothetical situation of MC without RTM.
|
|
View larger version (15K):
[in a new window]
|
Figure 2. An illustration of mathematical coupling (MC) due entirely to the effect of regression to the mean (RTM). (A) Observed y values plotted against observed x values, with the underlying relationship between them represented by the solid line. (B) A spurious correlation between z (= x - y) and x is shown; the solid line is the regression of z on x; this represents the hypothetical situation of MC as entirely RTM.
|
|
Copyright © 2002 Institutional Access Guidelines
