Figure 1
From: A hidden two-locus disease association pattern in genome-wide association studies
Illustration of unfaithfulness in association studies. There are three regression models in each scenario: Y ~ β1X1 + β2X2, 
and 
. In this figure, the marginal coefficient 
and 
are shown as projections (marked with bold red color) of Y on X1 and X2, respectively. (a) X1 is not correlated with X2. (b) X1 is positively correlated with X2. (c) X1 is negatively correlated with X2. (d) X1 is positively correlated with X2 but the sign of β1 is the opposite of the sign of β2. Scenario (c) and Scenario (d) illustrate unfaithfulness.