Data sources:
We obtained linked administrative data through IC/ES, formerly known as
the Institute of Clinical and Evaluative Sciences of Ontario.
Demographic data was available from the Ontario Registered Person
Database. The modified Charlson-Deyo comorbidity score was calculated
based on diagnoses registered for patients at hospital admissions in the
year preceding surgery 33. Severe obesity (class 3
obesity, BMI>40 according to the CDC classification) was
collected from unique surgical and anesthesia billing codes. Procedures
and treatments were extracted from the Ontario Health Insurance Plan
databases, used for documenting and billing all healthcare interactions
by providers, and from the Discharge Abstract Database maintained by the
Canadian Institute of Health Information (CIHI). Cancer diagnoses and
histologies, as well as stage information, is collected by Cancer Care
Ontario (CCO) in the Ontario Cancer Registry. CCO collects stage data
based on the staging criteria of the American Joint Committee on Cancer
or the Collaborative Stage initiative. For cases with more than one
valid stage value, a resolved “best stage” is derived based on a
pre-specified algorithm. Overall survival, from diagnosis to death, was
defined as the primary outcome for this analysis.
Exposure variables, including marginalization scores, income quintiles
and rural vs. urban residency, are neighborhood-based and assessed using
conversion software from Statistics Canada to match individuals’ postal
codes to small geographical units (Census Tracts and Dissemination Area)34. The Marginalization Score is an Ontario adaptation
of the Canadian Marginalization Index previously validated for health
research in Ontario and includes domains of material deprivation,
residential instability, dependency and ethnic concentration35. The residential instability index reflects housing
instability, number of residents per dwelling, family unit size and
composition. The material deprivation index includes information on
education, income, government support and unemployment. The ethnic
concentration index reflects the proportion of new immigrants
(< 5 years) in the community and those who self-identify as a
minority. The dependency index reflects the proportion of seniors and
dependent minors in the community; since uterine cancer is prevalent in
women in their 60s and 70s and is uncommon in young women, the
dependency scale was not considered relevant in this population and was
therefore not used in this analysis. Each of the three domains in the
index were evaluated separately and as a combined summary
marginalization score, as previously reported 35.
Marginalization indices are reported in quintiles, where quintile 5
reflects the highest degree of marginalization.