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Potential forms of bias and the direction that they may have influenced the results.
| Cause or Source of Bias | Direction of the Effect |
| Accuracy of "Usual Occupation" on Death Certificate | Either (most likely toward the null) |
| Only deceased individuals eligible as controls | Toward the null |
| Lack of specific job titles | Toward the null |
| Migration into and out of region | Toward the null |
| No information on length of employment | Toward the null |
| No information on specific chemicals used | Toward the null |
