SEER-Medicare: Defining the Date of Diagnosis & Treatment

The SEER program collects month and year of diagnosis. Therefore researchers sometimes are uncertain how to assign an exact date of diagnosis, often used as the index date for a period of observation. The figure below demonstrates the agreement between the SEER and Medicare claims regarding the month of diagnosis. There was nearly 90% agreement within one month of diagnosis.

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In other cases, researchers wish to assign a date when treatment began. For most cases, the Medicare claims can be used to identify the date for the first cancer-related treatment. However, not all persons will have a Medicare claim. In the event that there is no Medicare claim, researchers can impute a date from the SEER month of diagnosis, by assigning a point during the month of diagnosis, usually either the first or last day or midpoint. Use of sensitivity analysis can help to evaluate what impact, if any, use of different dates of diagnosis has on research findings.