County of residence at the time of diagnosis, as recorded in the OCISS, was categorized as follows: Appalachian/Rural, Metro, and Suburban.
Finally, given the high proportion of missing values on tumor size, number of lymph nodes or metastatic disease in the OCISS, we relied on SEER summary stage, rather than a detailed categorization of cancer stage.
Variables retrieved from OCISS included age (dichotomized as 40-64 and [greater than or equal to]65), race (white and nonwhite); and SEER summary stage (in situ, local, regional, distant, and unknown/unstaged).
Since the analysis did not consider patients with absent diagnosis or procedures in both OCISS and Medicaid files, other measures such as negative predictive value could not be determined.
A total of 234,195 and 230,474 women 40 years of age or older were enrolled for the Medicaid program at least for one month respectively in each of the study years 1997 and 1998, and a total of 8,648 and 9,250 incident cases of female breast cancer were identified through OCISS respectively in these study years.
In this study, we assessed the ability of Medicaid claims data to identify incident cases of breast cancer in the Medicaid population, using OCISS as the gold standard.
Of these, 26 cases matched successfully with OCISS records.
An important consideration in this study is that, despite its Silver Certification by the NAACCR, OCISS is not a reporting source that is as well established as SEER.
This approach seems to have been successful, as more than 89 percent of cases that were successfully linked with OCISS records were incident, rather than prevalent cases of cancer.
Future studies should use linked OCISS and Medicare--Medicaid files to assess the incremental benefit of adding Medicare claims in the analysis of evaluating the ability of claims data to ascertain incident cases of cancer in the dually eligible Medicare--Medicaid population.