Table 1. Characteristics of included studies.
| Authors (reference) | Indications for the index colonoscopy | Study design | Setting | Study period | Number of participantsa | Age at enrollment (years)b | Men (%) | Duration of follow-upc | Adjustments | Study qualityd |
| Eldridge et al. (60) | Screening | Prospective cohort | NIH-AARP Study, USA | 1995–2008 | 68,531 (22,780/45,751) | 50–71e | 62 | 11 yearsf | Age, sex, hormone replacement therapy, education, race, diabetes, family history of CRC, and healthy lifestyle score | 6 |
| Nishihara et al. (18) | Screening | Prospective cohort | Nurses' Health Study and Health Professionals Follow-up Study, USA | 1988–2012 | 88,902 (NA/NA) | Men: 42–77e Women: 32–57e | 35.7 | 1,841,586 person-years | Age, sex, calendar year of the questionnaire cycle, body mass index, smoking status, family history of CRC, status with respect to regular use of aspirin, physical activity level, red-meat intake, total caloric intake, alcohol intake, folate intake, calcium intake, multivitamin use, nonsteroidal antiinflammatory drug use, and cholesterol-lowering drug use | 7 |
| Brenner et al. (19)g | Screening | Case–control | Rhine-Neckar, Germany | 1993–2010 | 4,800 (2,516/2,284) | 70h | 59 | 1–10 yearse | Age, sex, county of residence, education, family history of CRC, smoking, body mass index, ever regular use of NSAIDs, ever use of hormone replacement therapy, and ever participation in a general health screening examination | 7 |
| Morois et al. (61) | Screening/diagnostic | Prospective cohort | E3N Study, France | 1990–2008 | 92,048 (37,459/54,589) | Colonoscopy group: 49.9±6.6 Control group: 48.8±6.6 | 0 | 15.4 yearsh | Age, physical activity, smoking status, family history of CRC, educational level, and body mass index | 7 |
| Jacob et al. (62) | Screening/diagnostic | Retrospective cohort | Ontario, Canada | 1996–2007 | 1,089,998 (86,837/1,003,161) | 62f | 45.1 | Incidence: 7 years Mortality: 5 years | Age, sex, comorbidity as measured by the Adjusted Diagnostic Groups case-mix system, neighborhood income quintile, rural residence, and PCP characteristics (age, sex, and country of medical education) | 9 |
| Wang et al. (63) | Screening/diagnostic | Retrospective cohort | SEER-Medicare, USA | 1998–2005 | 53,676 (12,266/41,410) | Colonoscopy group: 73.1±3.8 Control group: 73.3±4.0 | 39.3 | Colonoscopy group: 5 yearsf Control group: 5.3 yearsf | Age, sex, race, zip code, income and educational level, metropolitan county residence, endoscopist subspecialty, and SEER registry stratification | 7 |
| Baxter et al. (28) | Screening/diagnostic | Case–control | SEER-Medicare, USA | 1991–2007 | 37,099 (9,458/27,641) | Cases: 79.9 (70.0–89.9)i Controls: 79.8 (69.1–90.8)i | 42.6 | 9.4 yearsh | Age, sex, race, SEER registry, individual comorbid conditions, socioeconomic status, and urban/rural status | 6 |
| Kahi et al. (29) | Screening/diagnostic | Case–control | Veterans Affairs, USA | 1997–2007 | 2,492 (623/1,869) | 81.22±3.89 | 98.7 | 5.19 yearsf | Age, sex, race, NSAID use, and Charlson comorbidity index. | 5 |
| Mìller and Sonnenberg (64)j | Diagnostic | Case–control | Veterans Affairs, USA | 1981–1993 | 32,702 (16,351/16,351) | Cases (CC): 67.2±9.3 Cases (RC): 66.2±9.4 Controls: 57.0f | 97.8 | Cases (CC): 6.8 yearsf Cases (RC): 6.1 yearsf Controls: 7.1 yearsf | Age, sex, and race. | 4 |
| Mìller and Sonnenberg (65) | Diagnostic | Case–control | Veterans Affairs, USA | 1978–1992 | 20,889 (4,358/16,531) | Cases (CC): 69.1 (68.7–69.5)k Cases (RC): 68.3 (67.8–68.8)k Controls: 57.0 (57.0–57.1)k | 97.7 | Cases: 6.4 yearsf Controls: 8.3 yearsf | Age, sex, race, number of other colorectal procedures, procedures other than colorectal, length of coverage by the Department of Veterans Affairs, and presence of arthritis-related diseases. | 4 |
| Mulder et al. (66) | Diagnostic | Case–control | The Netherlands | 1996–2005 | 8,384 (594/7,790) | Cases: 69.5±11.9 Controls: 69.3±11.9 | 51.7 | 2.8 yearsh | Age, sex, calendar time, duration of follow-up before the date of diagnosis (index date), and IBD. | 7 |
CC, colon cancer; CRC, colorectal cancer; IBD, inflammatory bowel disease; NA, not available; NIH-AARP, National Institutes of Health American Association of Retired Persons; NSAID, nonsteroidal anti-inflammatory drug; RC, rectal cancer.
Numbers in parentheses represented number of participants in colonoscopy/control group (cohort studies), or number of cases/controls (case–control studies).
Values for age were presented as median (interquartile range) or mean±s.d. unless indicated otherwise.
Duration of follow-up for cohort studies, and duration from the exposure of colonoscopy to CRC occurrence/death for case–control studies.
Study quality was assessed based on the Newcastle–Ottawa Scale (range, 0–9 stars), details see Supplementary Appendices C and D online.
Range.
Mean.
Effect estimate was extracted from authors' reply letter by Brenner et al. (68).
Median.
Median (range).
Effect estimate was calculated by pooling the two separate estimates for colon and rectal cancer.
Mean (95% CI).