Figure 2.

Effect of span size on crude odds ratio map. We use a generalized additive model to estimate smoothed log odds as a function of space and converted to odds ratios using the whole population as a reference. An optimal span of 0.55, chosen by minimizing the AIC, shows the correct underlying pattern, a single area of elevated disease in the northeast quadrant. Under-smoothing (left) or over-smoothing (right) distorts the pattern.