Existing data sources for clinical epidemiology: Danish Cancer in Primary Care cohort

Figures & data

Figure 1 Patient flow for each subcohort and the CaP cohort in total (far right).

Note: c*, C01–C99, except C44, according to the Tenth Edition of the International Classification of Diseases (ICD-10).
Abbreviations: CaP, Danish Cancer in Primary Care; GP, general practitioner.

Table 1 Overview of information obtained from GP and patient questionnaires collected for the Danish Cancer in Primary Care cohort

Questionnaire	Data items (selected)	Geographical region	Period covered
GP-reported
Common	Key dates in the cancer diagnostic pathway (including date of first reported symptom, first presentation of symptoms in primary care, referral to hospital, first inpatient hospital investigation, date of diagnosis and date of treatment start, GP involved in diagnosing cancer).
Subcohort 1	Patient identifier, GP identifier, checklist of symptoms presented to the GP; the GP’s interpretation of symptoms at first presentation (alarm symptoms suggestive of cancer; symptoms suggestive of any serious illness; vague symptoms not directly suggestive of cancer or other serious illness), GP’s satisfaction with the health care provided, questions regarding the patient’s help-seeking approach (eg, frequent attending), questions about the patient’s comorbidity.	Former Danish County of Aarhus (now part of the Central Denmark Region)	September 1, 2004 to August 31, 2005
Subcohort 2	Patient identifier, GP identifier, GP’s interpretation of symptoms at first presentation (alarm symptoms or not), checklist of tests ordered by GP, checklist of tests were positive or negative, GP’s satisfaction with the health care provided, questions about the patient’s comorbidity.	Region of Southern Denmark and Central Denmark Region	October 1, 2007 to September 30, 2008
Subcohort 3	Patient identifier, GP identifier, checklist of symptoms presented to the GP, GP’s interpretation of symptoms at first presentation (alarm symptoms suggestive of cancer; symptoms suggestive of any serious illness; vague symptoms not directly suggestive of cancer or other serious illness), routes to diagnosis/use of standardized cancer patient pathways, checklist of possible quality deviations in the diagnostic pathway.	Denmark	May 1, 2010 to August 31, 2010
Patient-reported
Common	Patient identifier, dates of first reported symptom, first encounter with GP, referral, diagnosis and treatment plus involvement of other health care providers.
Subcohort 1	Patient identifier, self-reported socioeconomic characteristics (eg, marital status, number of children, education, occupation, household income and personal wealth, smoking and alcohol habits) and also psychological characteristics based on: a subscale from the Courtauld Emotional Control Questionnaire, the General Self-Efficacy Scale, a short 12-item version of the Marlow Crowne Social Desirability Scale, and 13 items from the Hopkins Symptom Check list.	Former Danish County of Aarhus (now part of Central Denmark Region)	September 1, 2004 to August 31, 2005
Subcohort 2	Patient identifier, patient’s self-perceived health status and quality of life based on: European Organisation for Research and Treatment of Cancer Quality of Life Questionnaire, patient’s evaluation of the GP using the Danish version of the European Patients Evaluate Practice questionnaire, patient’s social network based upon questions used in national surveys on patient-experienced quality of health care.	Region of Southern Denmark and Central Denmark Region	October 1, 2007 to September 30, 2008
Subcohort 3	Patient identifier. Main subjects covered were patient satisfaction and patient safety in relation to: access to diagnostics; involvement of patients and relatives; coordination and continuity of care, and information and communication. The questions were based on questions in subcohort 2 and additional add-on questions. The questionnaire was validated before use.	Denmark	May 1, 2010 to August 31, 2010

Abbreviation: GP, general practitioner.

Table 2 Overview of information from national registers linked to the Danish Cancer in Primary Care cohort

Register source	Register	Data extracted (selected)	Period covered*
a	Danish Civil Registration System	Patient identifier, date of birth, sex, parents’ civil registration number, status and dates of immigration, emigration and vital status	2000–2012
a	Danish Register of Causes of Death	Patient identifier and underlying causes of death	2000–2011
a	Danish National Patient Register	Patient identifier, dates of admission and discharge, data on hospital and department, diagnosis codes and surgical procedures	1994–2011
a	Danish Cancer Registry	Patient identifier, date of diagnosis, cancer site and cancer morphology, including TNM staging information	1943–2011
a	Danish Psychiatric Central Research Register	Patient identifier, admission and discharge dates, discharge diagnoses and hospital code	1994–2011
a	Danish National Prescription Registry	Patient identifier, code identifying prescribing physician, name of drug, ATC classification system code, number of packages, package size, doses and refill dates	2000–2011
a	Danish National Health Service Register	Patient identifier, personal information of provider such as name, address, sex, age and specialty (including fees and number of patients)	2003–2012
b	Statistics Denmark	Patient identifier, socioeconomic information such as origin, marital status, family circumstances, education and occupation, income, housing conditions, and geocodes	2000–2011

Notes: a, available from Statens Serum Institut (http://www.ssi.dk/English); b, available from Statistics Denmark (http://dst.dk/en/Statistik/dokumentation.aspx),

* as of September 2013.

Abbreviation: ATC, Anatomical Therapeutic Chemical.

Table 3 Participation rates according to demographic characteristics in the Danish Cancer in Primary Care cohort at baseline by subcohort, in total and listed for GP and patient surveys, respectively

	Subcohort 1 n=2,850		Subcohort 2 n=11,757		Subcohort 3 n=7,562		Total n=22,169
	GP	Patients	GP	Patients	GP	Patients	GP	Patients
Total	85.7	45.3	81.2	30.9	73.8	53.0	79.2	40.3
Sex
Male	84.1	43.0	79.9	27.3	71.9	50.3	77.6	37.3
Female	87.3	47.7	82.5	34.6	75.9	56.0	80.9	43.5
Age groups, years
18–44	87.3	60.5	82.5	36.6	76.3	47.9	81.2	44.0
45–54	87.9	57.7	84.9	37.8	74.3	56.2	81.4	47.1
55–64	85.1	50.5	82.0	38.2	73.5	59.4	79.5	46.9
65–74	86.3	47.0	80.8	33.8	73.6	58.1	78.9	43.9
≥75	84.4	31.7	79.3	18.1	73.4	41.6	78.1	27.6
Diagnosis
Colorectal	85.8	50.4	81.5	33.7	75.8	56.9	80.1	43.7
Lung	87.8	34.1	81.9	21.4	73.8	36.4	80.0	28.1
Melanoma	85.7	60.2	79.5	39.6	73.8	57.1	78.5	48.4
Breast	86.9	64.9	84.3	47.7	77.1	70.9	82.1	57.7
Prostate	81.5	55.0	78.0	29.4	69.9	60.9	75.5	43.2
Other	85.6	37.0	80.8	25.1	73.1	45.7	78.9	33.7
Clinical tumor stage
Local	88.7	57.1	81.3	37.9	73.5	61.9	79.4	48.7
Regional	90.1	58.1	82.5	43.3	74.2	61.2	80.7	51.0
Distant	88.0	33.5	81.9	18.5	74.2	36.6	80.1	26.5
Unknown	78.3	33.2	79.2	21.7	73.6	46.8	77.2	31.7
One-year survival
Alive	84.7	56.9	80.9	39.3	73.9	64.2	78.9	50.1
Dead	87.9	19.0	81.9	7.4	73.6	19.8	80.1	13.1
Comorbidity
None	86.1	49.6	81.1	34.6	73.8	57.8	79.2	44.4
Moderate	84.8	39.3	81.5	23.1	73.7	44.9	79.3	32.6
High	85.0	28.0	80.3	19.7	74.5	33.0	78.9	25.8
Educational level (ISCED)
Low (level 1 + level 2)	85.0	41.1	81.0	28.1	72.7	46.0	78.8	35.4
Medium (level 3 + level 4)	85.9	48.9	81.5	33.3	73.6	56.5	79.2	43.6
High (level 5 + level 6)	88.2	58.3	81.7	37.8	76.0	64.7	80.4	50.5
Missing	82.9	24.7	78.6	16.6	74.4	28.5	78.6	21.4
Tertiles of annual disposable OECD income (in EUR)
Lower third	84.9	35.3	80.4	24.5	73.1	41.6	78.4	31.8
Middle third	85.0	47.5	80.9	31.0	74.2	52.8	79.1	40.7
Upper third	87.2	59.7	82.6	40.3	74.1	65.0	80.2	51.3
Missing	85.8	1.5	76.8	0.3	73.7	21.1	78.9	1.3

Abbreviations: GP, general practitioner; OECD, Organisation for Economic Cooperation and Development; ISCED, International Standard Classification of Education.

Table 4 Baseline characteristics of study subjects in the Danish Cancer in Primary Care cohort according to GP and patient surveys, respectively

	Subcohort 1		Subcohort 2		Subcohort 3		Total
	GP n=2,442	Patient n=1,292	GP n=9,543	Patient n=3,635	GP n=5,581	Patient n=4,010	GP n=17,566	Patient n=8,937
	%	%	%	%	%	%	%	%
Sex
Male	49.5	47.8	49.6	44.4	53.7	49.4	49.9	47.1
Female	50.5	52.2	50.4	55.6	46.3	50.6	50.1	52.9
Age group, years
18–44	8.1	10.7	6.7	7.8	6.6	5.8	6.8	7.3
45–54	11.1	13.7	11.0	12.8	12.0	12.6	11.3	12.8
55–64	23.1	25.9	25.0	30.6	24.0	27.0	24.4	28.3
65–74	27.5	28.3	29.0	31.8	30.2	33.1	29.2	31.9
≥75	30.1	21.4	28.4	17.1	27.3	21.5	28.3	19.7
Diagnosis
Colorectal	13.3	14.8	14.0	15.2	14.2	14.9	14.0	15.0
Lung	14.7	10.8	13.8	9.5	13.4	9.2	13.8	9.6
Melanoma	5.7	7.5	4.9	6.5	5.1	5.4	5.1	6.2
Breast	13.6	19.2	17.4	25.8	17.6	22.5	16.9	23.4
Prostate	10.1	12.8	13.8	13.6	13.9	16.8	13.3	14.9
Other	42.6	34.8	36.1	29.4	35.8	31.1	36.9	31.0
GP involved in diagnosis
Yes	84.2	77.6	80.0	75.3	73.7	57.1	78.6	67.5
No	14.3	10.1	14.8	9.0	25.0	16.8	18.0	12.7
Unknown	1.5	12.3	5.2	15.7	1.3	26.1	3.5	19.9
Clinical tumor stage
Local	34.6	42.2	37.6	46.0	39.6	46.4	37.8	45.6
Regional	17.2	20.9	18.1	24.9	16.6	19.0	17.5	21.7
Distant	21.0	15.1	21.7	12.8	21.2	14.5	21.4	13.9
Unknown	27.2	21.8	22.6	16.2	22.7	20.1	23.3	18.8
One-year survival
Alive	68.7	87.2	73.5	93.7	75.0	90.6	73.3	91.4
Comorbidity
None	67.5	67.2	69.8	78.1	69.1	75.4	69.3	76.2
Moderate	25.1	25.3	24.6	18.3	24.1	20.4	24.5	19.8
High	7.4	7.5	5.6	3.6	6.8	4.2	6.2	4.0
Educational level (ISCED)
Low (level 1 + level 2)	36.9	37.2	42.4	38.6	37.5	33.0	40.1	35.4
Medium (level 3 + level 4)	34.2	34.1	34.8	37.3	37.9	40.4	35.7	38.6
High (level 5 + level 6)	19.2	18.7	17.4	21.1	20.6	24.4	18.6	23.0
Missing	9.7	10.1	5.4	3.0	4.1	2.2	5.6	3.0
Tertiles of annual disposable OECD income (in EUR)
Lower third	31.5	24.8	32.0	25.6	32.9	26.1	32.2	25.7
Middle third	31.5	33.3	32.2	32.4	33.4	33.1	32.5	32.8
Upper third	32.3	41.8	32.8	42.0	33.4	40.7	32.9	41.4
Missing	4.7	0.2	3.0	0.0	0.3	0.1	2.4	0.1

Abbreviations: GP, general practitioner; OECD, Organisation for Economic Cooperation and Development; ISCED, International Standard Classification of Education.