Table 3.

 Overview on observational studies: design aspects

Study	Country	Study design	Years (cases)	Lower gastrointestinal endoscopy			Covariates adjusted for or considered
				Reason	Type	Time frame (min, max)
Newcomb et al 19921	United States	Case-control	1979-88	Screening	Sigmoidoscopy	bd, ever	Sex, age, family history, duration of enrolment in health plan
Selby et al 19922	United States	Case-control	1971-87	Screening	Sigmoidoscopy	bd, 10 years	Sex, age, personal and family history, other screening examinations
Scheitel et al 199941	United States	Case-control	1970-93	Screening	Sigmoidoscopy	bd, 10 years	Sex, age, personal and family history, numbers of periodic health examinations and admissions to hospital
Slattery et al 200042	United States	Case-control	NR	Various*	Sigmoidoscopy	2 years, 12 years	Sex, age, family history, body mass index, physical activity, nutritional factors, acetylsalicylic acid or other non-steroidal anti-inflammatory drugs, HRT (in sensitivity analyses)
Newcomb et al 200343	United States	Case-control	1998-2002	Various*	Sigmoidoscopy	1 year, ever	Sex, age, education, family history, body mass index, smoking, HRT, number of previous tests
Cotterchio et al 200544	Canada	Case-control	1997-2000	Various*	Various†	1 year, ever	Sex, age, marital status, education, family history, medical conditions, body mass index, weight, physical activity, smoking, alcohol consumption, nutritional factors, acetylsalicylic acid or other non-steroidal anti-inflammatory drugs, HRT, other drugs
Blom et al 200845	Sweden	Cohort	1996-2004	Screening	Sigmoidoscopy	bd, 8 years	Sex, age
Kahi et al 200946	United States	Cohort‡	1989-2007	Screening	Colonoscopy	bd, 16 years	Sex, age
Manser et al 201247	Switzerland	Cohort	2001-07	Screening	Colonoscopy	bd, 7 years	Sex, age, profession, family history, body mass index, physical activity, smoking, nutritional factors, participation in general health screening examinations
Doubeni et al 201348	United States	Case-control	2006-08	Various*	Various†	3 months, 10 years	Sex, age, health plan enrolment, socioeconomic status, comorbidity, family history, other screening exposures
Brenner et al 201349	Germany	Case-control	2003-10	Various*	Colonoscopy	1 year, 10 years	Sex, age, education, family history, body mass index, smoking, acetylsalicylic acid or other non-steroidal anti-inflammatory drugs, HRT, participation in a general health screening examination
Nishihara et al 201350	United States	Cohort	1988-2012	Screening	Various†	bd, 25 years	Sex, age, family history, body mass index, physical activity, smoking, alcohol consumption, nutritional factors, acetylsalicylic acid or other non-steroidal anti-inflammatory drugs, HRT, other drugs

bd=before diagnosis (cases) or reference date (controls); NR=not reported; HRT=hormone replacement therapy.

*Various reasons analysed separately.

†Various types analysed separately.

‡Comparison with general population rather than comparison with unexposed group.