Bias magnification in ecologic studies: a methodological investigation

Table 5 Effect of non-differential exposure misclassification on individual and ecologic studies

The data are misclassified assuming the same sensitivity and specificity in each group, both equal to 0.8. Since there are no other sources of bias in this example, the crude individual and ecologic estimates of the RD are identical (0.7) for the correct data. For the misclassified data, the crude individual level estimate of the RD (0.42) is biased toward the null while the ecologic estimate (1.17) is biased away from the null. RD = risk difference; X _iand Y _iare the average exposure and average risk in group i.

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