SEER provides this specialized database in order to make available two calculated months fields: Months since last birthday and Months from diagnosis to treatment. The database is available in the frequency, survival, and case listing sessions in SEER*Stat for the November 2018 data submission.

For date information, such as date of birth or date of diagnosis, SEER only collects month and year.

Months Since Last Birthday

The month of birth is not available for research use because of confidentiality concerns. We calculated a months-since-last-birthday field, which can be used in conjunction with the age in years at diagnosis to derive the age in months at diagnosis.

This field is calculated as:

  • If Diagnosis month >= Birth month, then Months since last birthday = Diagnosis month - Birth month
    • For example, if born in January and diagnosed in March, Months since last birthday is 3 - 1 = 2
  • Else, Months since last birthday = (12 + diagnosis month) - Birth month.
    • For example, if born in November and diagnosed in January, Months since last birthday is (12 + 1) - 11 = 2

When the birth month and diagnosis month are the same, our estimate of age in months at diagnosis is as accurate as if day information were used in the calculation. However, when the months differ, our calculation is not accurate. For example, for a person with a January birth month and a February diagnosis month, the calculated months since last birthday would be one month. But in reality, it could be anywhere from 1 day to 59 days (assuming 30 days in every month). Therefore, in any calculated month after last birthday, about 50% of patients are in fact one month younger (assuming equal distribution of patients by birth month and diagnosis month). In aggregate, the number of patients with zero month is underestimated by 50% and the number of patients with 11 months is overestimated by 50%. Caution should be exercised in using this variable, given the limitation.

Months From Diagnosis to Treatment

The field is calculated as:

  • Months from diagnosis to treatment = ((Year initial treatment started * 12) + Month initial treatment started) - ((Year of diagnosis * 12) + Month of diagnosis)

Note that days are not available, so this calculation is not exact. If Months > 24 or a component of the date is unknown, we assign a value of blank for Months from diagnosis to treatment. The time is capped at 24 months after diagnosis because after 24 months, this would not typically be the first course of treatment.

The hormonal therapy, chemotherapy, and radiation variables are not complete in the SEER data, and if the treatment information is missing, the date of treatment is most likely missing as well. In some situations, the date represents the time that there was a decision not to treat (for example time that active follow up was started for prostate cancer).

How to Access the Calculated Months Fields Database

In order to access the custom database, you must already have access to SEER research data through SEER*Stat in client-server mode.

  • If you do not have access to SEER data in client-server mode, first request Access to the SEER data.
  • If you already have access, send an email to seercustomdata@imsweb.com to request access to the Calculated Months Fields Database.
    • Include your SEER*Stat username.
    • Since access to the Calculated Months Fields Database includes treatment data, a Data Use Agreement for SEER Radiation Therapy and Chemotherapy Information is required regardless of whether you intend to use treatment fields. If you have not already completed this DUA for the current submission, please complete and return it by email.
    • Add a brief description of your project and research goals in the email, including the types of analyses or statistics you will use, including how you would use treatment data, if you intend to use it.
    • Additionally, if you require access to the standard radiation/chemotherapy databases, please include this request in your email.