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Figure 6 | Environmental Health

Figure 6

From: Bias magnification in ecologic studies: a methodological investigation

Figure 6

Effect modification of the risk difference by group, illustrating Table 3. The solid black lines describing the individual-level information for the two groups have the same intercept (background risk q) but different slopes (risk differences b 0b 1). The crude estimate of the risk difference b c (blue line) lies between these two extremes. Relative to b w , the ecologic estimate of the risk difference b e (red line) is far more biased than the crude individual-level estimate b c . Both biases are in the same direction. b w (purple line) is the weighted average of the risk differences used in the bias magnification equation.

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