Fig. 2

Power of an association versus the number of controls per case as α decreases, as the power with 1 control per case increases from 0.1 to 0.2 to 0.3 to 0.5. Y-axis is on the probit scale to appropriately show meaningful differences in seemingly small power gains beyond 0.9; x-axis is on a log scale. Dotted horizontal lines indicate powers of 0.8 and 0.9