Four cancer cohorts were based on fee-for-service Medicare beneficiaries Part A and B eligible age 65 years and older for the period 2001 to 2005. We first identified beneficiaries who died, and then searched within defined periods prior to death for utilization events indicating that the patient had cancer. Cohorts were then evaluated on the basis of the number of beneficiaries assigned to the cohort and the likelihood that patients receiving hospice care with a principal diagnosis of cancer were also found within the cohort.
Duplicate claims and claims with an allowable charge of $0 were excluded from the analyses. Patients were classified as black or non-black, based on the work of others advocating this dichotomization, and availability of racial data in the Medicare claims dataset.2
The first cohort included decedents whose last inpatient stay from the MedPAR file had a principal diagnosis of cancer (Part A Definition) (ICD-9 codes: 140-208 or 239.0-239.9, excluding V codes) or with a secondary diagnosis of cancer considered to be metastatic or with a poor prognosis, based on previous work by Iezzoni et al.4
available online at www.liebertpub.com/jpm
). By using a secondary diagnosis of cancer identified as severe, we were able to capture those subjects admitted to the hospital for a potentially associated condition (e.g., pneumonia), even though the secondarily listed cancer diagnosis was the likely cause of subsequent death.
In the next two cohorts, we used diagnoses on physician and other clinician claims indicate the presence of cancer. This method included patients with cancer without a recent hospital discharge related to their terminal illness but who received outpatient care. These cohort definitions used a 20% beneficiary sample Carrier File of Medicare Part B physician claims (Part B thereafter). These files contain dates of service and associated diagnosis codes for each physician claim for an individual enrolled in Medicare Part B.5
The second cohort included patients who had claims with a primary diagnosis of cancer within the time frames specified above (Broad Definition). A diagnosis meeting these criteria had to occur two or more times, at least 6 days apart but not more than 120 days apart, with the later of the two claims occurring within the designated period from death. We then defined a third cohort using Part B data, but added a secondary diagnosis of a restricted set of severe cancers, similar to cohort 1 (Combined Definition).
Finally, we defined a fourth cohort based on the union of Part A and Part B claims from the sources above (Combined Part A Part B Definition). We selected a 20% beneficiary sample of the 100% Part A file comparable to the 20% Part B file. This sample was joined with the subjects in the Part B cohort that had a primary or secondary diagnosis of cancer using the methods outlined above.
We evaluated these cohorts four ways. First, we compared the number of deceased beneficiaries identified by each cohort with the U.S. vital records6
estimates of the number of cancer deaths in those over 65 for the target year. Second, if the cohort members died of cancer, we would expect that a reasonable proportion of them would receive hospice services. We calculated rates of hospice utilization for the entire cohort using the Medicare Hospice File. Hospice enrollment was defined as the “admission” to hospice services, regardless of location, nearest to death.
Third, we assumed that the principal diagnosis in a hospice admissions was the likely cause of death7
and then calculated the proportion of hospice patients with a cancer diagnosis that was also identified by our defined cohorts. Higher scores on this proportion indicate better “sensitivity” of a given cohort definition for detecting cases that died of cancer.
Finally, we calculated the proportions of true-positives within the cohorts. The denominator consisted of all members of a given cohort admitted to hospice, and the numerator the subset of those cases whose primary diagnosis for admission to hospice was cancer. Higher scores on this statistic indicated a given cohort definition identified a high proportion of true-positive cases in those receiving hospice care, and excluded cases that died of noncancer diagnoses.