Non-differential exposure misclassification (NDEM), illustrating Table 5. A. If there are no other sources of bias, the ecologic- and individual-level analyses of the correct data are the same. B. Suppose the dichotomous exposure data are misclassified with the same sensitivity and specificity in each group. Then the individual-level result (blue) is biased toward the null and the ecologic result (red) is biased away from the null. The average risks (Y
) in each group are unchanged but the average exposures move closer together. This causes the resulting ecologic regression line to have higher slope.