Table 1.

Definition of the study variables^*

Variable	Data source	Definition
Patient characteristics
Age	SEER	Age at diagnosis in years
Race	SEER	White, black, white Hispanic, other
Marital status	SEER	Married at time of diagnosis or not
Place of residence	SEER	SEER geographic region: San Francisco, Connecticut, Michigan, Hawaii, Iowa, New Mexico, Seattle, Utah, Georgia, San Jose (CA), Los Angeles
Socioeconomic status: income	2000 US Census	Available only at patient zip code level: median income in zip code of residence
Socioeconomic status: education	2000 US Census	Available only at patient zip code level: percentage of adults in zip code with <12 years of education
Comorbidity index	Medicare	Based on Klabunde modification of the Charlson index using inpatient, outpatient, and physician Medicare claims. The Charlson index is derived from a scoring system based on a count of certain comorbid diagnoses. Klabunde adaptation allows identification of comorbid diagnoses from Medicare inpatient and outpatient claims
No. of primary care physician visits	Medicare and AMA Masterfile	Calculated from number of physician visits on separate days as defined by the presence of an outpatient physician claim (excluding emergency room visits) for a face-to-face evaluation using †CPT codes of the form 99xxx. The UPIN associated with the claim was linked to AMA data to identify physician specialty as primary care (family practice, general internal medicine, general practice, or geriatricians)
Lower gastrointestinal endoscopy	Medicare	Any claim for ICD-9 procedure codes 45.23, 45.24, CPT codes 45330, 45355, 45378, or HCPCS codes G0104, or G0105
Diabetes mellitus	Medicare	One inpatient claim or two outpatient–physician claims in any position with ICD-9 diagnosis codes 250.xx, 357.2,362.0-362.0x,366.41,790.2
Obesity	Medicare	Any claim for ICD-9 diagnosis codes 278.00, 278.01, 783.1, 783.6
Cancer characteristics (at diagnosis)
Stage	SEER	Prostate cancer: using clinical T stage from SEER Extent of Disease coding; categorized as T1, T2, T3, T4, unknown. Colorectal cancer: using SEER historical staging system; categorized as in situ, localized, regional or distant spread, or unknown
Grade	SEER	Prostate or colorectal cancer: SEER grading information; categorized as well differentiated, moderately differentiated, poorly differentiated, undifferentiated, or unknown
Site (colorectal only)	SEER	Based on site code definitions; categorized as cecum, appendix, ascending colon, hepatic flexure, transverse colon, splenic flexure, descending colon, sigmoid colon, large intestine not otherwise specified, rectosigmoid junction and rectum
Androgen deprivation
Orchiectomy	Medicare	Any claim with CPT codes 54520, 54521, 54522, 54530, or 54535; or ICD-9 procedure code 62.4
GnRH agonist	Medicare	Any claim with HCPCS codes J9202, J1950, J9217, J9218, or J9219
Months of GnRH agonist therapy	Medicare	Calculated from each instance of a GnRH agonist HCPCS J-code noted on separate days. GnRH agonists are generally administered as depot injections with the dosage given depending on the intended duration of the regimen; usually once a month, once every 3-month or once every 4-month regimens. The intended duration for a given injection was determined first from the unit designation (1, 3, or 4) of the “carrier miles/time/units/serv count” field of the physician services claims or if unavailable, from the “revenue center unit count” field of the outpatient claims
Study outcome
Incident colorectal cancer	SEER or Medicare	From SEER: site codes indicating colorectal cancer diagnosis following diagnosis of prostate cancer. From Medicare claims algorithm: ICD-9 diagnosis codes 153.x, 154.0, 154.1, 230.3, 230.4 in any position in at least one inpatient claim or at least two (on different days) outpatient or physician claims with no claims in preceding 2 years

^*AMA = American Medical Association; CPT = Current Procedural Terminology; GnRH = gonadotropin-releasing hormone; HCPCS = Healthcare Common Procedure Coding System; ICD-9 = International Classification of Diseases, Ninth revision; SEER = Surveillance, Epidemiology and End Results; UPIN = unique physician identification number.